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149 records · Page 9Linked to original sources
USGS2023

Volcanic aquifers of Hawaiʻi—Contributions to assessing groundwater availability on Kauaʻi, Oʻahu, and Maui

The volcanic aquifers of the Hawaiian Islands supply water to 1.46 million residents, diverse industries, and a large component of the U.S. military in the Pacific. Groundwater also supplies fresh water that supports ecosystems in streams and near the coast. Hawaii’s aquifers are remarkably productive given their small size, but the capacity of the islands to store fresh groundwater is limited because each island is surrounded by seawater, and salt water underlies much of the fresh groundwater. The amount of fresh groundwater available for human use from Hawai‘i’s volcanic aquifers is constrained by the consequences of groundwater withdrawal. Restrictions placed on these consequences can translate to limitations on groundwater availability. Changes in recharge resulting from changes in land cover or climate can alter the effect of withdrawals. This study uses numerical models of the volcanic aquifers of the islands of Kaua‘i, O‘ahu, and Maui to quantify the consequences of historical and plausible future withdrawals and changes in recharge. The study compares the results of model simulations of multiple scenarios of historical and projected future withdrawal and recharge. Results of the simulations using the groundwater models of the islands of Kaua‘i, O‘ahu, and Maui have implications for other islands in Hawai‘i. Since the first modern water well was drilled in Hawai‘i in 1879, total groundwater withdrawals on Kaua‘i, O‘ahu, and Maui have risen to nearly 400 million gallons per day. Model simulations indicate that these withdrawals have caused reductions in groundwater discharge to streams and springs, reductions in groundwater discharge to the ocean, changes in subsurface flow between sectors within an island, lowering of groundwater levels, and rise of the interface between fresh water and salt water in the aquifers. Future increases in withdrawals will increase the severity of the consequences. Changes in recharge can alter the effect of withdrawals—increases in recharge can offset the consequences of withdrawals, whereas decreases in recharge can exacerbate the effects of withdrawals. This study quantifies the consequences of withdrawals for past and plausible future circumstances. The models can be used to test other circumstances. Limits placed on the consequences of withdrawals—such as restrictions to protect stream or coastal ecosystems that rely on groundwater discharge and limitations on water-level decline and rise of the freshwater-saltwater interface to protect the productivity of existing wells—can translate to limits on groundwater availability from Hawai‘i’s volcanic aquifers. Setting acceptable limits to the consequences of groundwater withdrawal is also a critical part of assessing groundwater availability. Once these limits are set, numerical models can be used to quantify the amount of water that can be withdrawn within those limits and thereby inform management decisions that seek to balance the need to limit the consequences of groundwater withdrawals with the need to develop water for human use.

Hawaii↗
USGS2019

Managing effects of drought and other water resource challenges in Alaska and the Pacific Northwest

This is a Cooperator Report. As such, there is no specific abstract. The physical, ecological, and social environments of Alaska and the Pacific Northwest (PNW) region of the United States are extremely diverse. Alaska ranges from the Arctic Ocean and the very cold, dry environments of the North Slope to the cool and very rainy coastal North Pacific region of Southeast Alaska. Most precipitation falls as snow at higher elevations. In Arctic Alaska, average annual temperature is 14.6 F, and average annual precipitation is 11 inches. By contrast, in Southeast Alaska, average annual temperature is 35.8 F, and annual average precipitation is 143 inches. The PNW, defined here as Idaho, Oregon, and Washington, ranges from the Pacific Coast (annual precipitation of 200 inches) to interior semi-arid regions (annual precipitation of 8 inches). Precipitation patterns in the PNW are strongly governed by orographic phenomena, with high, persistent snowpack in the higher mountains (e.g., record annual snowfall of 1,130 in at Mount Baker, Washington in 1999-2000). Ecosystems in the PNW include productive temperate coniferous forests near the Pacific coast and along the (wet) west slope of the Cascade Range, less productive mixed-conifer forest along the (dry) east slope of the Cascades and in interior mountain ranges, and sagebrush-steppe and shrublands at lower elevations in much of the interior and mountain valleys. Large rivers and thousands of smaller tributaries form an extensive network of riparian, wetland, and estuarine systems that provide both critical hydrologic function and biological diversity at broad and fine spatial scales. Although Alaska and the Pacific Northwest differ in important physical, ecological, and social features, the importance of natural resources is evident in both regions. Water is important for wildlife and people. Water provides critical habitat for salmon, which are culturally and economically valuable species. Timber production has declined in recent decades. Recreation has emerged as a major revenue source.

Alaska, Oregon, Washington↗
USGS2018

Spatial distribution of estuarine diamond-backed terrapins (Malaclemys terrapin) and risk analysis from commercial blue crab (Callinectes sapidus) trapping at the Savannah Coastal Refuges Complex, USA

The diamond-backed terrapin (Malaclemys terrapin) is a small estuarine turtle distributed along the Atlantic and Gulf Coasts of the USA. Terrapin populations are declining throughout their range and one of the main causes is mortality by drowning as bycatch in commercially-fished blue crab (Callinetes sapidus) traps (aka pots). We conducted head counts of terrapins and documented the distribution and number of crab pots on the Savannah Coastal Refuges Complex in southeast Georgia, USA. Using an index for representing relative degree of crabbing pressure, we conducted a spatial risk analysis for each of the four refuges surveyed. We fit a series of generalized linear mixed effect models to test hypotheses about the scale (creek scale vs. refuge/island scale) at which terrapin relative abundances respond to crab trapping. Several creeks were found to be at high risk of terrapin mortality from crab pots. Areas with low terrapin head counts may be a result of past crab pot mortality. The best model relating terrapin counts to crab trapping revealed a negative effect of crab pots calculated at the refuge/island scale and included a positive association between cloud cover and terrapin counts. The estimated effect of crab pot number at the refuge/island scale suggests that an increase in crab pot density of one pot per creek is associated with a 74.6% decline in terrapin head counts, underscoring the sensitivity of terrapin populations to crab pot mortality. Mitigation of this mortality factor via redesigned crab traps with bycatch reduction devices may be necessary to maintain healthy terrapin populations on the refuges.

Georgia↗
USGS2023

Observations of coastal circulation, waves, and sediment transport along West Maui, Hawaiʻi (November 2017– March 2018), and modeling effects of potential watershed restoration on decreasing sediment loads to adjacent coral reefs

Terrestrial sediment discharging from watersheds off West Maui, Hawaiʻi, has been documented as a primary stressor to local coral reefs, causing coral reef health to decline. The U.S. Geological Survey acquired and analyzed physical oceanographic and sedimentologic field data off the coast of West Maui to calibrate and validate physics-based, numerical hydrodynamic and sediment transport models of the study area developed by Deltares. These models simulated terrestrial sediment transport and dispersal from West Maui watersheds into coastal waters and how terrestrial sediment affects nearby coral reefs under different oceanographic forcing and watershed restoration scenarios. Wave energy and near-bed turbidity are positively correlated in the field observations, illustrating a process not captured by the model simulations in which sediment already deposited on the seabed is resuspended by wave action and subsequently transported by prevailing currents. In the model simulations, large waves during flood events led to a decrease in suspended-sediment concentrations. Notably, however, the model results only consider sediment entering coastal waters from five stream sources and do not simulate sediment already present on the seabed. The model simulations project that the Honokeana and Māhinahina coral reefs would experience the greatest reduction in sediment impacts from theoretical watershed restoration. Additionally, when large waves coincide with flood events, post-storm sedimentation generally decreases in the nearshore region, but increases in the region offshore of the reefs. The measured and modeled sediment dynamics demonstrate a demarcation between the coral reefs sheltered within embayments (Honolua reef) or behind points (Wahikuli reef) and those along the relatively open coastline between Kapalua and Kāʻanapali (Kapalua, Honokeana, Māhinahina, and Honokōwai reefs). The sheltered sites are affected by terrestrial sediment from single stream mouths, where most sediment is delivered within hours of a flood (rain) event. Once this sediment enters the nearshore, it settles out and remains within the reef area for a prolonged period owing to a lack of wave or current-driven bed shear stress. Thus, the primary effect of sediment on the reefs within these sheltered areas is sedimentation. In contrast, coral reefs along the unsheltered (or “open”) section of coastline (between Kapalua and Kāʻanapali) are more exposed to waves and terrestrial sediment from multiple stream sources. At these reefs, fine-grained terrestrial sediment can rarely settle but instead remains in suspension. Thus, even long after a flood event has occurred, these sites chronically experience light attenuation from suspended sediment. These analyses underscore the importance of understanding how coastal ocean waves and circulation can lead to different sediment dynamics and stressors for coral reefs along the same region of the West Maui coastline. These differing factors indicate that the most effective watershed restoration and mitigation strategies may vary among the different coral reefs and streams. An important next step is to determine how the science of this study can support management goals for these coral reefs: what are target reductions of sedimentation, suspended-sediment concentrations, or the resulting light attenuation? Then, using the coupled hydrodynamic-sediment model, we can examine which watershed restoration scenarios in each stream will best achieve those targets.

Hawaii↗
USGS2025

Quantifying sea otter abundance, distribution, habitat use, and foraging intake in Cook Inlet, Alaska

Following near extirpation from the fur trade, sea otters ( Enhydra lutris ) have returned to occupy lower Cook Inlet since the 1950s, or earlier, with numbers increasing to ~11,000 and ~9,000 on the west and east side, respectively, by 2017. Northward range expansion on the west side has been negligible for decades with few animals found north of Kamishak Bay, while northward expansion on the east side has been more pronounced in recent decades. The reasons for these contrasting distribution patterns are not certain. Possible explanations for lack of expansion on the west side included 1) poor sea otter habitat north of Kamishak Bay; 2) adequate habitat north of Kamishak Bay but no incentive for sea otters to move north because of abundant food in Kamishak Bay, and/or sea otters discouraged from moving north of Kamishak Bay; 3) seasonal ice formation; or 4) seasonal presence of killer whales. This project was designed to document current sea otter abundance and distribution in lower Cook Inlet, including seasonal variation, and evaluate drivers of habitat use and foraging conditions, including how these overlap with Bureau of Ocean Energy Management (BOEM) Lease Sale blocks. We found that the probability of sea otter presence in lower Cook Inlet was significantly related to depth and distance from shore with the highest probabilities of sea otter presence in areas ~7–8 kilometers (km) from shore in water ~20–30 meters (m) deep. Historical survey data suggest sea otter distribution has not changed dramatically since 2002, and while we detected significant seasonal changes including due to presence of heavy sea ice, the seasonal changes were modest and primarily related to locations with consistent winter ice formation on the west side of lower Cook Inlet. Overall, throughout the year, sea otters appeared to be utilizing most of the habitat within the 40-m depth contour on the east side of lower Cook Inlet, including Kachemak Bay. Sea otters on the west side reside largely within Kamishak Bay. Because of the shallow bathymetry of lower Cook Inlet, sea otters consistently occurred farther offshore than in many other areas of Alaska. The presence of sea otters, including females with pups, in these offshore waters indicates that sea otters can forage productively in these open water areas. Importantly, we documented that sea otters, including females with pups, occurred in most of the eastern BOEM lease blocks including the original Lease Sale 244 blocks 7064, 7114, 6162, 6310, 6360, 6410, 6458 and 6457. The relinquishments for these 7 leases were effective September 17, 2024: OCS-Y-02434 (block # 7064), OCS-Y-02435 (7114), OCS-Y-02436 (6162), OCS-Y-02438 (6357), OCS-Y-02442 (6407), OCS-Y02446 (6457), OCS-Y-02447 (6458) https://www.boem.gov/sites/default/files/documents/environment/Map%20of%20Active%20Leases%20 Cook%20Inlet%20OCS_0.pdf Regarding differential northward expansion on the east and west side of lower Cook Inlet, we found that wind and water circulation patterns make winter sea ice more prominent on the west side, but this had minimal effects on sea otter distribution. In addition, although there have been observations of killer whale ( Orcinus orca ) predation on sea otters in Cook Inlet, we did not see behavioral or distributional evidence that it was prevalent enough to have strong effects on sea otter habitat use. Benthic surveys using a remotely operated vehicle (ROV) indicated that epibenthic substrate and biological community heterogeneity differed between areas with and without otters, suggesting that these factors may explain the current distribution of otters within lower Cook Inlet. However, ROV surveys cannot assess infaunal prey abundance, making assessments of the role of prey availability difficult. The existence of a healthy Pacific razor clam ( Siliqua patula ) fishery along western lower Cook Inlet along the Lake Clark coast north of Kamishak Bay suggests there may still be a resource base for eventual expansion of sea otters into this area. Our shore-based forage observations indicated that sea otters exist near carrying capacity densities relative to nearshore prey resources. However, our distribution model suggests the bulk of the population lives offshore beyond our ability to observe their feeding activity. The fact that sea otters are a consistent presence in offshore areas suggests that prey resources in these areas were relatively abundant in comparison to nearshore prey resources, making foraging in offshore areas, with water depths of 0–40 m, energetically profitable. Prey types in these offshore areas of lower Cook Inlet likely included epifauna such as crabs and large urchins, in addition to infaunal clams based on the soft substrate habitat types that characterize lower Cook Inlet. Collectively, our results suggest that sea otters occupy most areas of lower Cook Inlet with appropriate benthic habitat types and prey resources, which includes areas within BOEM Lease Sale blocks. With the exception of the Lake Clark coast, sea otters may be approaching a food- and habitat-limited distribution and carrying capacity, suggesting that the current status of sea otters in lower Cook Inlet is likely to remain similar in the absence of significant changes to prey, habitat, predation, or anthropogenic disturbance.

Alaska↗