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Geology topics

Linda A. Deegan

Publications and source records attributed to Linda A. Deegan.

11 recordsLinked to original sources
USGS2025

Relationship-centered engagement bridges the divide between science and management, and enhances climate adaptation

The rapid pace of climate change demands changes in management practices. Despite abundant climate adaptation research, the implementation of climate adaptation can lag in the management space. In the present article, we argue that relationship-centered engagement—establishing and maintaining relationships among researchers and natural resource managers—is critical for bridging the research–management gap. We evaluated researcher–manager partnerships within the US Northeast Climate Adaptation Science Center and identified three cultural shifts that institutions, funders, researchers, and managers could adopt to boost the odds of translating findings into action: acknowledging and supporting the central role of relationships in creating and implementing actionable science, lengthening funding timelines to better support establishing and maintaining relationships, and aligning institutional rewards to support relationship building. A renewed focus on relationships can lead to more diverse and effective partnerships that bridge knowledge to practice and hasten adaptation to climate change.

BioScience↗
USGS2025

Distribution and disturbances of ditches across salt marshes of the Northeast U.S. with implications for management and restoration

Effective management of valuable coastal systems, such as salt marshes requires an understanding of the complex stressors influencing their continued threat of drowning. However, efforts to determine the effects of one potential stressor, ditches, have produced diverging results complicating management efforts. Ditches (linear trenches dug to drain salt marshes for agriculture and mosquito control) alter salt marsh hydrology, but their effects on widescale marsh function and degradation are poorly understood. We created a dataset of visible ditches and summarized ditch densities (length of ditches over area) for salt marshes of the Northeast U.S. to evaluate ditching against vulnerability metrics, including elevation and the unvegetated to vegetated marsh ratio (UVVR). We identified a scale dependency in which the larger/coarser the spatial scale of analysis, the greater the fraction of ditched salt marshes. Scale dependence explains discrepancies between previously determined ditch indices. In terms of effects on marsh vulnerability, relative elevation was not influenced by visible ditch presence. Ditch densities affected UVVR, exhibiting a multiple threshold behavior. When present at low densities, ditches have little effect on ponding; yet as ditch densities increase, UVVR (i.e., ponding) increases. The relationship between ditching and UVVR reverses at the highest ditch densities, with ponding substantially decreasing. The multiple threshold vulnerability response of Northeast salt marshes to the hydrologic influences imposed by ditching suggests restoration strategies should consider the degree of ditching rather than simply ditching presence.

Connecticut, Delaware, Maine, Maryland, Massachuse↗
USGS2023

Long-term changes in concentrations and yield of riverine dissolved silicon from the poles to the tropics

Riverine exports of silicon (Si) influence global carbon cycling through the growth of marine diatoms, which account for ∼25% of global primary production. Climate change will likely alter river Si exports in biome-specific ways due to interacting shifts in chemical weathering rates, hydrologic connectivity, and metabolic processes in aquatic and terrestrial systems. Nonetheless, factors driving long-term changes in Si exports remain unexplored at local, regional, and global scales. We evaluated how concentrations and yields of dissolved Si (DSi) changed over the last several decades of rapid climate warming using long-term data sets from 60 rivers and streams spanning the globe (e.g., Antarctic, tropical, temperate, boreal, alpine, Arctic systems). We show that widespread changes in river DSi concentration and yield have occurred, with the most substantial shifts occurring in alpine and polar regions. The magnitude and direction of trends varied within and among biomes, were most strongly associated with differences in land cover, and were often independent of changes in river discharge. These findings indicate that there are likely diverse mechanisms driving change in river Si biogeochemistry that span the land-water interface, which may include glacial melt, changes in terrestrial vegetation, and river productivity. Finally, trends were often stronger in months outside of the growing season, particularly in temperate and boreal systems, demonstrating a potentially important role of shifting seasonality for the flux of Si from rivers. Our results have implications for the timing and magnitude of silica processing in rivers and its delivery to global oceans.

Global Biogeochemical Cycles↗
USGS2021

Land use change influences ecosystem function in headwater streams of the Lowland Amazon Basin

Intensive agriculture alters headwater streams, but our understanding of its effects is limited in tropical regions where rates of agricultural expansion and intensification are currently greatest. Riparian forest protections are an important conservation tool, but whether they provide adequate protection of stream function in these areas of rapid tropical agricultural development has not been well studied. To address these gaps, we conducted a study in the lowland Brazilian Amazon, an area undergoing rapid cropland expansion, to assess the effects of land use change on organic matter dynamics (OM), ecosystem metabolism, and nutrient concentrations and uptake (nitrate and phosphate) in 11 first order streams draining forested ( n = 4) or cropland ( n = 7) watersheds with intact riparian forests. We found that streams had similar terrestrial litter inputs, but OM biomass was lower in cropland streams. Gross primary productivity was low and not different between land uses, but ecosystem respiration and net ecosystem production showed greater seasonality in cropland streams. Although we found no difference in stream concentrations of dissolved nutrients, phosphate uptake exceeded nitrate uptake in all streams and was higher in cropland than forested streams. This indicates that streams will be more retentive of phosphorus than nitrogen and that if fertilizer nitrogen reaches streams, it will be exported in stream networks. Overall, we found relatively subtle differences in stream function, indicating that riparian buffers have thus far provided protection against major functional shifts seen in other systems. However, the changes we did observe were linked to watershed scale shifts in hydrology, water temperature, and light availability resulting from watershed deforestation. This has implications for the conservation of tens of thousands of stream kilometers across the expanding Amazon cropland region.

Tanguro Ranch↗
USGS2021

Riparian forests buffer the negative effects of cropland on macroinvertebrate diversity in lowland Amazonian streams

Riparian forests regulate stream ecosystems and biodiversity. Therefore, changes to riparian structure may threaten stream ecosystem function by triggering taxonomic and functional changes to aquatic communities. Because macroinvertebrate assemblages are sensitive to environmental changes, they can be effective indicators of stream integrity in disturbed landscapes. To assess the role of riparian forests in maintaining tropical stream communities in areas experiencing large-scale watershed disturbance, we quantified the taxonomic and functional response of stream macroinvertebrate communities to forest clearing in the southeastern Amazon’s agricultural frontier, a region experiencing widespread deforestation. Our results show that watershed deforestation can lead to significant changes in macroinvertebrate richness and community composition. We found a predominance of shredders in forested watersheds; scrapers in cropland watersheds with riparian forests; and collector-filterers in cropland watersheds without riparian forest buffers. Taxonomic composition was controlled by available organic material in forested watersheds and by periphyton in cropland sites regardless of whether they had a riparian buffer. Our results show that the clearing of riparian forests alters food sources supporting aquatic food webs, leading to ecosystem-level shifts through changes in light and temperature dynamics that affect aquatic communities in areas with intense land-use change such as the southeastern Amazon.

Tanguro Ranch↗
USGS2016

Discontinuities concentrate mobile predators: Quantifying organism-environment interactions at a seascape scale

Understanding environmental drivers of spatial patterns is an enduring ecological problem that is critical for effective biological conservation. Discontinuities (ecologically meaningful habitat breaks), both naturally occurring (e.g., river confluence, forest edge, drop-off) and anthropogenic (e.g., dams, roads), can influence the distribution of highly mobile organisms that have land- or seascape scale ranges. A geomorphic discontinuity framework, expanded to include ecological patterns, provides a way to incorporate important but irregularly distributed physical features into organism–environment relationships. Here, we test if migratory striped bass ( Morone saxatilis ) are consistently concentrated by spatial discontinuities and why. We quantified the distribution of 50 acoustically tagged striped bass at 40 sites within Plum Island Estuary, Massachusetts during four-monthly surveys relative to four physical discontinuities (sandbar, confluence, channel network, drop-off), one continuous physical feature (depth variation), and a geographic location variable (region). Despite moving throughout the estuary, striped bass were consistently clustered in the middle geographic region at sites with high sandbar area, close to channel networks, adjacent to complex confluences, with intermediate levels of bottom unevenness, and medium sized drop-offs. In addition, the highest striped bass concentrations occurred at sites with the greatest additive physical heterogeneity (i.e., where multiple discontinuities co-occurred). The need to incorporate irregularly distributed features in organism–environment relationships will increase as high-quality telemetry and GIS data accumulate for mobile organisms. The spatially explicit approach we used to address this challenge can aid both researchers who seek to understand the impact of predators on ecosystems and resource managers who require new approaches for biological conservation.

Ecosphere↗
USGS2013

What happens in an estuary doesn't stay there: patterns of biotic connectivity resulting from long term ecological research

The paucity of data on migratory connections and an incomplete understanding of how mobile organisms use geographically separate areas have been obstacles to understanding coastal dynamics. Research on acoustically tagged striped bass (Morone saxatilis) at the Plum Island Ecosystems (PIE) Long Term Ecological Research site, Massachusetts, documents intriguing patterns of biotic connectivity (i.e., long-distance migration between geographically distinct areas). First, the striped bass tagged at PIE migrated southward along the coast using different routes. Second, these tagged fish exhibited strong fidelity and specificity to PIE. For example, across multiple years, tagged striped bass resided in PIE waters for an average of 1.5-2.5 months per year (means: 51-72 days; range 2-122 days), left this estuary in fall, then returned in subsequent years. Third, this specificity and fidelity connected PIE to other locations. The fish exported nutrients and energy to at least three other coastal locations through biomass added as growth. These results demonstrate that what happens in an individual estuary can affect other estuaries. Striped bass that use tightly connected routes to feed in specific estuaries should have greater across-system impacts than fish that are equally likely to go anywhere. Consequently, variations in when, where, and how fish migrate can alter across-estuary impacts.

Massachusetts↗
USGS2011

Seasonal use of a New England estuary by foraging contingents of migratory striped bass

Using acoustic telemetry on migratory striped bass Morone saxatilis in Plum Island Estuary (PIE), Massachusetts, we found that striped bass (335–634 mm total length) tagged in the spring and summer of 2005 ( n = 14) and 2006 ( n = 46) stayed in the estuary for an average of 66.0 d in 2005 and 72.2 d in 2006. Striped bass spent the most time in two specific reaches: middle Plum Island Sound and lower Rowley River. In both years, three different use-groups of striped bass were observed in PIE. Short-term visitors ( n = 24) stayed in the estuary only briefly (range = 5–20 d). Two groups of seasonal residents stayed for more than 30 d, either in the Rowley River ( n = 14) or in Plum Island Sound ( n = 22). Within PIE, the two seasonal-resident use-groups may be foraging contingents that learn how to feed efficiently in specific parts of the estuary. These distinct within-estuary use patterns could have different implications for striped bass condition and prey impact.

Massachusetts↗
USGS2010

Diversity in destinations, routes and timing of small adult and sub-adult striped bass Morone saxatilis on their southward autumn migration

Almost three-quarters of the 46 young adult and sub-adult striped bass Morone saxatilis that were acoustically tagged in Plum Island Estuary, Massachusetts, U.S.A., in the summer of 2006 were detected in one or more southern coastal arrays during their autumn migration. On the basis of the trajectories along which these M. saxatilis moved from feeding to overwintering areas, three migratory groups emerged. After leaving Plum Island Estuary, about half of the fish were detected only in a mid-latitude array, Long Island Sound. The other half of the tagged fish were detected during autumn and winter in a more southern array, the Delaware Estuary. This latter group of fish may have used two routes. Some travelled to the Delaware Estuary through Long Island Sound while other fish may have taken a second, more direct, coastal route that did not include Long Island Sound. Consequently, a seemingly homogeneous group of fish tagged at the same time in the same non-natal feeding location exhibited a diversity of southward movement patterns that could affect population-level processes. These three groups that differed in overwintering location and migration route could be movement contingents with migratory connectivity.

Massachusetts↗
USGS2009

Use of non-natal estuaries by migratory striped bass (Morone saxatilis) in summer

For most migratory fish, little is known about the location and size of foraging areas or how long individuals remain in foraging areas, even though these attributes may affect their growth, survival, and impact on local prey. We tested whether striped bass (Morone saxatilis Walbaum), found in Massachusetts in summer, were migratory, how long they stayed in non-natal estuaries, whether observed spatial patterns differed from random model predictions, whether fish returned to the same area across multiple years, and whether fishing effort could explain recapture patterns. Anchor tags were attached to striped bass that were caught and released in Massachusetts in 1999 and 2000, and recaptured between 1999 and 2007. In fall, tagged striped bass were caught south of where they were released in summer, confirming that fish were coastal migrants. In the first summer, 77% and 100% of the recaptured fish in the Great Marsh and along the Massachusetts coast, respectively, were caught in the same place where they were released. About two thirds of all fish recaptured near where they were released were caught 2-7 years after tagging. Our study shows that smaller (400-500 mm total length) striped bass migrate hundreds of kilometers along the Atlantic Ocean coast, cease their mobile lifestyle in summer when they use a relatively localized area for foraging (<20 km 2 ), and return to these same foraging areas in subsequent years.

Fishery Bulletin↗