Geology topics

L. R. Brown

Publications and source records attributed to L. R. Brown.

At least 19 recordsLinked to original sources

USGS2008

Managing water to protect fish: A review of California's environmental water account, 2001-2005

The Sacramento-San Joaquin Delta, the landward reach of the San Francisco Estuary, provides habitat for threatened delta smelt, endangered winter-run Chinook salmon, and other species of concern. It is also the location of huge freshwater diversion facilities that entrain large numbers of fish. Reducing the entrainment of listed fishes into these facilities has required curtailment of pumping, reducing the reliability of water deliveries. We reviewed the first 5 years (2001–2005) of the Environmental Water Account (EWA), a program instituted to resolve conflicts between protecting listed fishes and providing a reliable water supply. The EWA provided fishery agencies with control over 0.2–0.4 km 3 of water to be used for fish protection at no cost to users of exported water, and fish agencies guaranteed no disruption of water supply for fish protection. The EWA was successful in reducing uncertainty in water supply; however, its contribution to the recovery of listed fishes was unclear. We estimated the effectiveness of the EWA to be modest, increasing the survival of winter-run Chinook salmon by 0–6% (dependent on prescreen mortality), adult delta smelt by 0–1%, and juvenile delta smelt by 2–4%. Allocating EWA water for a single life stage of one species could provide larger gains in survival. An optimally allocated EWA of equal size to the median of the first 5 years could increase abundance of juvenile delta smelt up to 7% in the springs of dry years. If the EWA is to become a long-term program, estimates of efficacy should be refined. If the program is to be held accountable for quantitative increases in fish populations, it will be necessary to integrate scientific, possibly experimental, approaches.

California↗

USGS2008

Distribution of algae in the San Joaquin River, California, in relation to nutrient supply, salinity and other environmental factors

1. The taxonomic composition and biomass of the phytoplankton and the taxonomic composition of the phytobenthos of the San Joaquin River and its major tributaries were examined in relation to water chemistry, habitat and flow regime. Agricultural drainage and subsurface flow contribute to a complex gradient of salinity and nutrients in this eutrophic, 'lowland type' river. 2. Because of light-limiting conditions for growth, maintenance demands of the algae exceed production during summer and autumn in the San Joaquin River where there is no inflow from tributaries. In contrast to substantial gains in concentration of inorganic nitrogen and soluble reactive phosphorus during the summer of normal-flow years, net losses of algal biomass (2-4 ??g L -1 day -1 chlorophyll a) occurred in a mid-river segment with no significant tributary inflow. However, downstream of a large tributary draining the Sierra Nevada, a substantial net gain in algal biomass (6-11 μg L -1 day -1 ) occurred in the summer, but not in the spring (loss of 1-6 μg L -1 day -1 ) or autumn (loss of 2-5 ??g L -1 day -1 ). 3. The phytoplankton was dominated in summer by 'r-selected' centric diatoms (Thalassiosirales), species both tolerant of variable salinity and widely distributed in the San Joaquin River. Pennate diatoms were proportionally more abundant (in biomass) in the winter, spring and autumn. Abundant taxa included the diatoms Cyclotella meneghiniana, Skeletonema cf. potamos, Cyclostephanos invisitatus, Thalassiosira weissflogii, Nitzschia acicularis, N. palea and N. reversa, and the chlorophytes Chlamydomonas sp. and Scenesdesmus quadricauda. Patterns in the abundance of species indicated that assembly of the phytoplankton is limited more by light and flow regime than by nutrient supply. 4. The phytobenthos was dominated by larger, more slowly reproducing pennate diatoms. Few of the abundant species are euryhaline. The diatoms Navicula recens and Nitzschia inconspicua and cyanophytes, Oscillatoria spp., were the principal late-summer benthic species upstream in the mainstem and in drainages of the San Joaquin Valley. Many of the other abundant diatoms (Amphora veneta, Bacillaria paxillifer, Navicula symmetrica, Nitzschia amphibia, N. fonticola, N. palea, Pleurosigma salinarum) of late-summer assemblages in these segments also are motile species. While many of these species also were abundant in segments downstream of confluences with rivers draining the Sierra Nevada, the relative abundance of prostrate (Cocconeis placentula var. euglypta, Navicula minima) and erect or stalked (Achnanthidium deflexum, Achnanthes lanceolata, Gomphonema kobayasii, G. parvulum var. lagenula) diatoms and Stigeoclonium sp. was greater in these lower San Joaquin River segments. 5. A weighted-averaging regression model, based on salinity and benthic-algal abundance in the San Joaquin River and segments of its major tributaries within the San Joaquin Valley, yielded a highly significant coefficient-of-determination (r 2 = 0.84) and low prediction error between salinity inferred from the species and that observed, indicating that salinity tolerance is a primary constraint on growth and assembly of the phytobenthos. The same measures of predictability indicated poor performance of a model based on inorganic nitrogen. However, with a greater representation of tributaries (including segments within the Sierra Nevada foothills) in the sample set, an inorganic nitrogen model also yielded a highly significant coefficient-of-determination (r 2 = 0.87) and low prediction error between the species-inferred and the observed concentration. As with the salinity model (r 2 = 0.94) for the enlarged data set, a systematic difference (increased deviation of residuals) existed at high inorganic nitrogen concentrations. These results indicate substantial interaction between salinity and inorganic nitrogen as constraints on the structure of benthic-algal communities of the San Joaquin River basin.

California↗

USGS2008

Species composition and habitat associations of benthic algal assemblages in headwater streams of the Sierra Nevada, California

Despite their trophic importance and potential importance as bioindicators of stream condition, benthic algae have not been well studied in California. In particular there are few studies from small streams in the Sierra Nevada. The objective of this study was to determine the standing crop of chlorophyll-a and benthic algal species assemblages present in the small 1st- and 2nd-order streams of the Kings River Experimental Watersheds (KREW, watersheds of Bull, Providence, Duff, and Teakettle Creeks) and determine the associations of these measures with stream habitat. We collected samples of benthic algae from rock substrata in September 2002 (7 sites) and 2005 (the same 7 sites plus 5 additional sites). Habitat and water-quality data were collected concurrently. Chlorophyll-a values ranged from 0.2 to 3.2 mg??m-2. Chlorophyll-a in the Bull Creek watershed was generally lower than in the other watersheds. Benthic algal assemblages were dominated by diatoms and cyanobacteria. We collected 79 taxa of diatoms in 2002 and 126 taxa in 2005. Diatom taxa richness in individual samples ranged from 15 to 47. Nonmetric multidimensional scaling analysis of arcsine square-root transformed proportional abundances of diatoms identified 3 groups of sites. Bull Creek sites were generally different from other sites (group 1), and the sites from Bull Creek were different in 2002 (group 2) and 2005 (group 3). Five taxa appeared to be particularly important in distinguishing groups: Achnanthidium minutissimum, Cocconeis placentula, Eunotia incisa, Eunotia pectinalis var. minor, and Planothidium lanceolatum. Elevation, water temperature, pH, specific conductance, and canopy were habitat variables correlated with the differences in diatom assemblages among sites. Our results provide a valuable baseline for future studies of benthic algae in Sierra Nevada headwater streams and will be particularly important in understanding the effects of different forest restoration management strategies being tested in the KREW project.

Western North American Naturalist↗

USGS2007

Littoral fish assemblages of the alien-dominated Sacramento-San Joaquin Delta, California, 1980-1983 and 2001-2003

We analyzed monthly boat electrofishing data to characterize the littoral fish assemblages of five regions of the Sacramento-San Joaquin Delta (northern, southern, eastern, western, and central), California, during two sampling periods, 1980-1983 (1980s) and 2001-2003 (2000s), to provide information pertinent to the restoration of fish populations in this highly altered estuary. During the 1980s, almost 11,000 fish were captured, including 13 native species and 24 alien species. During the 2000s, just over 39,000 fish were captured, including 15 native species and 24 alien species. Catch per unit effort (CPUE) of total fish, alien fish, and centrarchid fish were greater in the 2000s compared with the 1980s, largely because of increased centrarchid fish CPUE. These differences in CPUE were associated with the spread of submerged aquatic vegetation (SAV), particularly an alien aquatic macrophyte Egeria densa. Native fish CPUE declined from the 1980s to the 2000s, but there was no single factor that could explain the decline. Native fish were most abundant in the northern region during both sampling periods. Nonmetric multidimensional scaling indicated similar patterns of fish assemblage composition during the two sampling periods, with the northern and western regions characterized by the presence of native species. The separation of the northern and western regions from the other regions was most distinct in the 2000s. Our results suggest that native fish restoration efforts will be most successful in the northern portion of the Delta. Management decisions on the Delta should include consideration of possible effects on SAV in littoral habitats and the associated fish assemblages and ecological processes.

California↗

USGS2007

Aquatic vertebrate assemblages of the upper Clear Creek Watershed, California

We sampled streams in the Upper Clear Creek Watershed in northwestern California in fall 2004 and fall 2005 to document assemblages of aquatic vertebrates and to provide resource managers with information on the importance of these assemblages in terms of regional biodiversity. We used single-pass backpack electrofishing to sample 15 sites in fall 2004 and the same 15 sites plus 4 new sites in fall 2005. We captured 10 fish taxa and 2 species of larval amphibians. Seven of the fish taxa were native species. Of the exotic species, only brook trout (Salvelinus fontinalis) occurred at more than 1 site. Ordinations by nonmetric multidimensional scaling indicated a gradient from sites with rainbow trout (Oncorhynchus mykiss), Pacific giant salamander (Dicamptodon tenebrosus), and tailed frog (Ascaphus truei) to sites dominated by riffle sculpin (Cottus gulosus), California roach (Hesperoleucas symmetricus), and Sacramento sucker (Catostomus occidentalis). The gradient in species composition was associated with changes in elevation, gradient, discharge, and substrate. The Upper Clear Creek Watershed represents a unique area of overlap between the North Coast California amphibian fauna and the Central Valley fish fauna with a notable paucity of exotic fishes and amphibians. Preservation of the integrity of native aquatic assemblages is an important goal for aquatic resource management in the region; our results provide a critcial baseline to gauge future management actions.

California↗

USGS2006

Relation of fish communities to environmental conditions in urban streams of the Wasatch Front, Utah

Twenty-eight sites along the Wasatch Front, north central Utah, representing the range ot urban land use intensity for wadeable streams of the area, were sampled in September 2000. Fish communities were assessed by single-pass electrofishing, and physical habitat and water-quality characteristics were measured. On average, nonnative species comprised 54% of species richness and 53% of relative abundance, although only Salmo trutta and Pimephales promelas were very abundant at any 1 site. Salmo trutta and Catostomus platyrhynchus, a native species, were the most widely distributed and abundant species captured. Analysis of fish communities using nonmetric multidimensional scaling (NMDS) revealed a community gradient from sites dominated by Salmo trutta and Cottus species (C. bairdi, C. beldingi) to sites dominated by Catostomus platyrhynchus. Sites dominated by C. platyrhynchus were smaller in size and had less habitat cover, smaller average substrate size, higher concentrations of dissolved constituents, and higher water temperature than sites dominated by S. trutta. Sites dominated by C. platyrhynchus were located in more intensely urbanized watersheds at lower elevations. Stream size and associated instream habitat availability appear to limit S. trutta distribution and abundance, while native species appear more tolerant of decreased water quality and increased water temperatures in more urbanized streams. Most of the study sites are affected by development of water infrastructure for human water use (e.g., dams and diversions), and this infrastructure may play a role in dispersal of species.

Western North American Naturalist↗

USGS2005

Can diet-dependent factors help explain fish-to-fish variation in thiamine-dependent early mortality syndrome?

To provide insight into the reasons why offspring of certain salmonine females exhibit early mortality syndrome (EMS) in the Great Lakes whereas others do not, we measured the egg concentrations of potential biochemical markers (stable isotopes of nitrogen and carbon, fatty acid signatures, and lipid-soluble carotenoids and vitamins) that are indicative of differing food web and trophic structure. To corroborate the presence of EMS, we also measured the egg content of thiamine vitamers. For all the stocks of coho salmon Oncorhynchus kisutch and Chinook salmon O. tshawytscha we studied, there was a very high correspondence between EMS and low concentrations of unphosphorylated thiamine in unfertilized eggs. For salmonine stocks in the Platte River, Thompson Creek, and the Swan River, Michigan, small but significant shifts occurred in measures of egg carotenoids, retinoids, ??15N depletion, and fatty acid profiles of fish producing normal offspring relative to those exhibiting EMS. Egg thiamine concentrations in Chinook salmon from the Little Manistee River, Michigan, in the low-EMS group were only marginally above the threshold for EMS induction. Along with this small thiamine differential, there was no evidence of differing food web or dietary factors between EMS-positive and normal Chinook salmon from the Little Manistee River. Further investigations are required to determine the potential dietary sources for the observed differences in biochemical markers between EMS-positive and normal fish. These findings are generally consistent with the hypothesis that a more diverse forage base may help to limit overall dietary content of species that contain thiaminase, such as alewives Alosa pseudoharengus, and may lead to improved embryonic survival for feral salmonids. ?? Copyright by the American Fisheries Society 2005.

Journal of Aquatic Animal Health↗

USGS2005

Effect of sample handling on thiamine and thiaminolytic activity in alewife

Alewives Alosa pseudoharengus were collected to evaluate handling and processing conditions that may affect the measurement of their thiamine-thiaminase content. Fish were captured by otter trawl, and reference samples of live fish were quick-frozen on dry ice immediately following capture. Other samples were placed on wet ice (4??C) or held in ambient lake water (21.5??C) for periods of up to 5 h before freezing. Total thiamine levels for reference samples averaged 26 nmol/g and consisted of 66, 15, and 19% thiamine pyrophosphate (TPP), thiamine monophosphate (TMP), and unphosphorylated thiamine (Th), respectively. After 120 min at either 4??C or 21.5??C, total thiamine concentrations were lower. At 21.5??C, the TPP proportion had decreased by 30 min and the proportion as Th increased after 60 min. In the groups sampled after 5 h, total thiamine concentrations were not altered but the proportion of TPP was lower and that of Th was higher than in reference samples. The stability of thiamine in thawed muscle samples from previously frozen alewives was poor (40% loss by 1 h at 22??C and 30% loss by 2 h at 4??C). Thiaminase activity averaged 5,975 pmol??g wet weight -1??min-1 in reference samples. In fresh-caught alewives, thiaminase activities were remarkably consistent throughout the sampling period. At 4??C, thiaminase activity in muscle tissue from previously frozen alewives was stable for the entire investigation period. At 25??C, the activity initially increased by 40% after 60 min but then decreased to 50% of initial value after 5 h. We conclude that sampling times greater than 25 min could cause some changes in the various thiamine forms and net loss in total thiamine. The thiamine content in previously frozen alewife samples is highly labile, requiring low temperatures during processing for analysis. ?? Copyright by the American Fisheries Society 2005.

Journal of Aquatic Animal Health↗

USGS2005

Effectiveness of egg immersion in aqueous solutions of thiamine and thiamine analogs for reducing early mortality syndrome

Protocols used for therapeutic thiamine treatments in salmonine early mortality syndrome (EMS) were investigated in lake trout Salvelinus namaycush and coho salmon Oncorhynchus kisutch to assess their efficacy. At least 500 mg of thiamine HCl/L added to egg baths was required to produce a sustained elevation of thiamine content in lake trout eggs. Thiamine uptake from egg baths was not influenced by a pH ranging from 5.5 to 7.5 or by a water hardness between 2 and 200 mg CaCO3/L. There was poorer thiamine uptake when initial thiamine levels were low, suggesting that current treatment regimes may not be as effective when thiamine levels are severely depressed and that higher treatment doses are necessary. Exposure of eggs to the more lipid-soluble thiamine analog allithiamine (1,000 mg/L) during water hardening increased egg thiamine levels by 1.5-2.5 nmol/g and was completely effective at reversing EMS. Another more lipid-soluble thiamine analog, benfotiamine (100 mg/L), reduced EMS but did not produce detectable increases in egg thiamine content. Although benfotiamine may be more effective than thiamine at mitigating EMS, it is more expensive than thiamine HCl or allithiamine. In addition, there still needs to be a more thorough examination of dose-response relationships. We conclude that allithiamine is an alternative to the use of thiamine in egg baths as a therapeutic treatment for salmonid EMS. ?? Copyright by the American Fisheries Society 2005.

Journal of Aquatic Animal Health↗

USGS2005

Thiamine and thiaminase status in forage fish of salmonines from Lake Michigan

Dietary sources of thiamine (vitamin B 1 ) and thiamine-degrading enzymes (thiaminases) are thought to be primary factors in the development of thiamine deficiency among Great Lakes salmonines. We surveyed major forage fish species in Lake Michigan for their content of thiamine, thiamine vitamers, and thiaminase activity. Concentrations of total thiamine were similar ( P ≤ 0.05) among most forage fishes (alewife Alosa pseudoharengus , bloater Coregonus hoyi , spottail shiner Notropis hudsonius , deepwater sculpin Myoxocephalus thompsonii , yellow perch Perca flavescens , ninespine stickleback Pungitius pungitius , and round goby Neogobius melanostomus ) and slightly lower in rainbow smelt Osmerus mordax . Concentrations of total thiamine were all above the dietary requirements of coldwater fishes, suggesting the thiamine content of forage fish is not the critical factor in the development of thiamine deficiency in Lake Michigan salmonines. Thiamine pyrophosphate was the predominant form of thiamine in most species of forage fish, followed by free thiamine and thiamine monophosphate. Total thiamine was slightly greater in summer collections of alewife and rainbow smelt than in spring and fall collections, but the same was not true for bloater. Thiaminase activity varied among species and was greatest in gizzard shad Dorosoma cepedianum , spottail shiner, alewife, and rainbow smelt. Thiaminase activity in alewife varied among collection locations, season (greatest in spring), and size of the fish. Size and condition factors were positively correlated with both total thiamine and thiaminase activity in alewife. Thus, thiamine and thiaminase activity in forage fishes collected in Lake Michigan varied among species, seasons, year caught, and size (or condition). Therefore, multiple factors must be considered in the development of predictive models for the onset of thiamine deficiency in Great Lakes salmonines. Most importantly, thiaminase activity was great in alewives and rainbow smelt, suggesting that these prey fish are key causative factors of the thiamine deficiency in Great Lakes salmonines.

Journal of Aquatic Animal Health↗

USGS2005

Thiamine content and thiaminase activity of ten freshwater stocks and one marine stock of alewives

Alewives Alosa pseudoharengus contain thiaminase activity that has been implicated in the development of a thiamine deficiency and associated effects in salmonines of the Great Lakes basin. Little is known about the factors that regulate thiaminase activity in alewives. We sampled alewives of uniform size (60-120 mm) during the summer of 1998 from the Gulf of St. Lawrence, seven of New York's Finger Lakes, one inland lake in Ontario, and two Great Lakes to assess possible relationships among thiamine, lipid content, fish abundance, lake morphometry, lake productivity, freshwater residency, and thiaminase activity. Thiaminase activity varied significantly among the 11 locations but was unrelated to thiamine concentration, which did not vary significantly. Alewife thiaminase activity in the Finger Lakes was negatively related to lipid content and positively related to measures of lake size (e.g., area, volume, and maximum depth). Activity in the one marine stock sampled in the Gulf of St. Lawrence was comparable to the highest values observed in the 10 freshwater stocks examined. Variation in alewife thiaminase activity has the potential to affect the extent of a thiamine deficiency associated with salmonines who feed on alewives as well as the viability of their offspring.

Big Rideau Lake, Finger Lakes, Gulf of St. Lawrenc↗

USGS2005

Invaders eating invaders: Exploitation of novel alien prey by the alien shimofuri goby in the San Francisco Estuary, California

The shimofuri goby (Tridentiger bifasciatus), which is native to Asian estuaries, was recently introduced to the San Francisco Estuary, California, USA. We conducted gut content analyses to examine the goby's feeding ecology in this highly invaded estuary. Shimofuri gobies were generalist predators on benthic invertebrates, consuming seasonally abundant prey, especially amphipods (Corophium spp.). In addition, shimofuri goby utilized two novel prey items not exploited by other resident fishes - hydroids (Cordylophora caspia) and barnacle (Balanus improvisus) cirri, both of which are alien. The shimofuri goby's feeding ecology appears well-suited to the fluctuating environment of the San Francisco Estuary and may partially explain observed increases in shimofuri goby abundance compared with declines in populations of some native species. ?? Springer 2005.

Biological Invasions↗

USGS2004

Effect of outflow on spring and summertime distribution and abundance of larval and juvenile fishes in the upper San Francisco Estuary

We analyzed data on spring and summertime larval and juvenile fish distribution and abundance in the upper San Francisco Estuary (SFE), California between 1995 and 2001. The upper SFE includes the tidal freshwater areas of the Sacramento-San Joaquin Delta downstream to the euryhaline environment of San Pablo Bay. The sampling period included years with a variety of outflow conditions. Fifty taxa were collected using a larval tow net. Two common native species, delta smelt Hypomesus transpacifucus and longfin smelt Spirinchus thaleichthys, and four common alien taxa, striped bass Morone saxatilis, threadfin shad Dorosoma petenense, gobies of the genus Tridentiger, and yellowfin goby Acanthogobins flavimanus, were selected for detailed analysis. Outflow conditions had a strong influence on the geographic distribution of most of the species, but distribution with respect to the 2 psu isohaline (X2) was not affected. The distribution patterns of delta smelt, longfin smelt, and striped bass were consistent with larvae moving from upstream freshwater spawning areas to down-stream estuarine rearing areas. There were no obvious relationships of outflow with annual abundance indices. Our results support the idea of using X2 as an organizing principle in understanding the ecology of larval fishes in the upper SFE. Additional years of sampling will likely lead to additional insights into the early life history of upper SFE fishes. ?? Copyright by the American Fisheries Society 2004.

American Fisheries Society Symposium↗

USGS2003

Relations between introduced fish and environmental conditions at large geographic scales

Data collected from 20 major river basins between 1993 and 1995 as part of the US Geological Survey's (USGS) National Water-Quality Assessment (NAWQA) Program were analyzed to assess patterns in introduced and native fish species richness and abundance relative to watershed characteristics and stream physicochemistry. Sites (N = 157) were divided into three regions-northeast, southeast, and west- to account for major longitudinal differences in precipitation/runoff and latitudinal limits of glaciation that affect zoogeographic patterns in fish communities. Common carp (Cyprinus carpio) and largemouth bass (Micropterus salmoides) were the most frequently collected introduced fish species across all river basins combined. Based on the percentage of introduced fish species, the fish communities most altered by the presence of introduced fish occurred in the western and northeastern parts of the US. Native fish species richness was not an indicator of introduced fish species richness for any of the three regions. However, in the west, introduced fish species richness was an indicator of total fish species richness and the abundance of introduced fish was negatively related to native fish species richness. Some relations between introduced fish species and environmental conditions were common between regions. Increased introduced fish species richness was related to increased population density in the northeast and southeast; increased total nitrogen in the northeast and west; and increased total phosphorous and water temperature in the southeast and west. These results suggest that introduced fish species tend to be associated with disturbance at large geographic scales, though specific relations may vary regionally. ?? 2003 Elsevier Science Ltd. All rights reserved.

Ecological Indicators↗

USGS2002

Fish communities of the Sacramento River Basin: Implications for conservation of native fishes in the Central Valley, California

The associations of resident fish communities with environmental variables and stream condition were evaluated at representative sites within the Sacramento River Basin, California between 1996 and 1998 using multivariate ordination techniques and by calculating six fish community metrics. In addition, the results of the current study were compared with recent studies in the San Joaquin River drainage to provide a wider perspective of the condition of resident fish communities in the Central Valley of California as a whole. Within the Sacramento drainage, species distributions were correlated with elevational and substrate size gradients; however, the elevation of a sampling site was correlated with a suite of water-quality and habitat variables that are indicative of land use effects on physiochemical stream parameters. Four fish community metrics - percentage of native fish, percentage of intolerant fish, number of tolerant species, and percentage of fish with external anomalies - were responsive to environmental quality. Comparisons between the current study and recent studies in the San Joaquin River drainage suggested that differences in water-management practices may have significant effects on native species fish community structure. Additionally, the results of the current study suggest that index of biotic integrity-type indices can be developed for the Sacramento River Basin and possibly the entire Central Valley, California. The protection of native fish communities in the Central Valley and other arid environments continues to be a conflict between human needs for water resources and the requirements of aquatic ecosystems; preservation of these ecosystems will require innovative management strategies.

Environmental Biology of Fishes↗

USGS2000

Macroinvertebrate assemblages on woody debris and their relations with environmental variables in the lower Sacramento and San Joaquin River drainages, California

Data from 25 sites were used to evaluate associations between macroinvertebrate assemblages on large woody debris (snags) and environmental variables in the lower San Joaquin and Sacramento River drainages in California as part of the U.S. Geological Survey's National Water Quality Assessment Program. Samples were collected from 1993 to 1995 in the San Joaquin River drainage and in 1996 and 1997 in the Sacramento River drainage. Macroinvertebrate taxa were aggregated to the family (or higher) level of taxonomic organization, resulting in 39 taxa for analyses. Only the 31 most common taxa were used for two-way indicator species analysis (TWINSPAN) and canonical correspondence analysis (CCA). TWINSPAN analysis defined four groups of snag samples on the basis of macroinvertebrate assemblages. Analysis of variance identified differences in environmental and biotic characteristics among the groups. These results combined with the results of CCA indicated that mean dominant substrate type, gradient, specific conductance, water temperature, percentage of the basin in agricultural land use, percentage of the basin in combined agricultural and urban land uses, and elevation were important factors in explaining assemblage structure. Macroinvertebrate assemblages on snags may be useful in family level bioassessments of environmental conditions in valley floor habitats.

Environmental Monitoring and Assessment↗

USGS2000

Fish communities and their associations with environmental variables, lower San Joaquin River drainage, California

Twenty sites in the lower San Joaquin River drainage, California, were sampled from 1993 to 1995 to characterize fish communities and their associations with measures of water quality and habitat quality. The feasibility of developing an Index of Biotic Integrity was assessed by evaluating four fish community metrics, including percentages of native fish, omnivorous fish, fish intolerant of environmental degradation, and fish with external anomalies. Of the thirty-one taxa of fish captured during the study, only 10 taxa were native to the drainage. Multivariate analyses of percentage data identified four site groups characterized by different groups of species. The distributions of fish species were related to specific conductance, gradient, and mean depth; however, specific conductance acted as a surrogate variable for a large group of correlated variables. Two of the fish community metrics - percentage of introduced fish and percentage of intolerant fish - appeared to be responsive to environmental quality but the responses of the other two metrics - percentage of omnivorous fish and percentage of fish with anomalies - were less direct. The conclusion of the study is that fish communities are responsive to environmental conditions, including conditions associated with human-caused disturbances, particularly agriculture and water development. The results suggest that changes in water management and water quality could result in changes in species distributions. Balancing the costs and benefits of such changes poses a considerable challenge to resource managers.

Environmental Biology of Fishes↗

USGS1997

Concentrations of chlorinated organic compounds in biota and bed sediment in streams of the San Joaquin Valley, California

Samples of resident biota and bed sediments were collected in 1992 from 18 sites on or near the floor of the San Joaquin Valley, California, for analysis of 33 organochlorine compounds. The sites were divided into five groups on the basis of physiographic region and land use. Ten compounds were detected in tissue, and 15 compounds were detected in bed sediment. The most frequently detected compound in both media was p,p'-DDE. Concentrations of ??DDT (sum of o,p'- and p, p' forms of DDD, DDE, and DDT) were statistically different among groups of sites for both tissue and sediment (Kruskal- Wallis, p < 0.05). Concentrations in both media were highest in streams draining the west side of the valley. Concentrations of ??DDT in tissue were significantly correlated with specific conductance, pH, and total alkalinity (p < 0.05), which are indicators of the proportion of irrigation return flows in stream discharge. Concentrations in sediment on a dry-weight basis were not correlated with these water-quality parameters, but total organic carbon (TOC) normalized concentrations were significantly correlated with specific conductance and pH (p < 0.05). Regressions of the concentration of ??DDT in tissue, as a function of ??DDT in bed sediment, were significant and explained up to 76% of the variance in the data. The concentration of ??DDT in sediment may be related to mechanisms of soil transport to surface water with bioavailability of compounds related to the concentration of TOC in sediment. The results of this study did not indicate any clear advantage to using either bed sediment or tissues in studies of organochlorine chemicals in the environment. Some guidelines for protection of fish and wildlife were exceeded. Concentrations of organochlorine chemicals in biota, and perhaps sediment, have declined from concentrations measured in the 1970s and 1980s, but remain high compared to other regions of the United States.

Archives of Environmental Contamination and Toxico↗