Browsing by Subject "lake"

An abstract of a dissertation: As humans increasingly alter the surface geomorphology of the Earth, a multitude of artificial aquatic systems have appeared, both deliberately and accidentally. Human modifications to the hydroscape range from alteration of existing waterbodies to construction of new ones. The extent and ecosystem services of these systems are underexplored, but likely substantial and changing. Instead of simply accepting that artificial ecosystems have intrinsically low values, environmental scientists should determine what combination of factors, including setting, planning and construction, subsequent management and policy, and time, impact the condition of these systems. Scientists, social scientists, and policymakers should more thoroughly evaluate whether current study and management of artificial aquatic systems is based on the actual ecological condition of these systems, or judged differently, due to artificiality, and consider resultant possible changes in goals for these systems. The emerging recognition and study of artificial aquatic systems presents an exciting and important opportunity for science and society.

Irrigation ditches are ubiquitous features of water networks in rural and urban settings in drylands, and are thus potentially important habitats within the modern hydroscape. The habitat value of ditches and other artificial systems depends on whether these systems respond to local and watershed-scale land use in similar ways to natural features, or whether artificial origin inherently constrains a system's ecological condition. The ditches and creeks of Bishop, California are fed by water from the same minimally developed watershed on the Eastern slope of the Sierra Nevada Mountains, and so served to test whether artificial and natural waters in the same watershed setting and with shared water can provide similar habitat. We sampled benthic macroinvertebrates at 52 sites within the town, stratified by substrate and season. Communities varied by substrate and season as expected, but did not differ significantly between artificial and natural streams. Instead, both types of streams changed as water flowed from undeveloped desert through town, suggesting that irrigation ditches respond to local urbanization in much the same way that natural streams do. Differences in finer-scale spatial structure of community similarity suggest that community assembly processes may differ between natural and artificial channels, but potential mechanisms for these differences are unclear. This study demonstrates that artificial aquatic systems may have substantial ecological value, and suggests that the poor condition of many artificial aquatic systems may reflect stressful watershed settings rather than something intrinsic to their artificiality.

The drainage ditches of the North Carolina Coastal Plain do not merely degrade wetlands; they themselves have ecological structural characteristics of wetlands. We surveyed 32 agricultural, freeway, and forested ditch reaches across this region for hydrologic indicators, soil organic matter, and plants. All showed some hydrologic indicators and had some soil organic matter, with easterly, swampy forests having the most, though with substantial variation across all and few significant differences between types. All had hydrophytic herbaceous plant communities in the sense of at least half their percent cover belonging to obligate, facultative wetland, or facultative taxa. These herbaceous communities differed significantly across site types (F=3.25, d.f.= 2, p=0.001), and responded to both landscape-level factors like nearby development coverage and local-level factors like apparent mowing. Sample sites were not well mapped in well-used federal aquatic databases; the National Hydrography Dataset only included one on a “CanalDitch” flow line, and the National Wetlands Inventory only included two within “partially drained/ditched” areas, and none as individual “excavated” features. Others were mis-categorized, but neither database included any highway sampling sites. Despite this limited information about extent, variation and management impact suggests that human potential to impact wetland structure of these manmade aquatic ecosystems throughout the North Carolina Coastal Plain, and beyond, could be large.

Artificial lakes are a dominant aquatic ecosystem type, but the processes controlling their condition are under-explored. Here we use structural equations modeling to compare the formation of algal blooms and associated water quality issues in 1,045 artificial and 870 natural lakes in the United States using the U.S. Environmental Protection Agency’s National Lakes Assessment data. We compare chemical and physical measurements associated with water quality and the relationships between them, and find that the processes are significantly different between natural and artificial lakes, in a way that suggests impacts of interference with thermal stratification through dam management in reservoirs. However, both the overall processes and the distributions of the data are roughly similar between the two origin types, and between 2007 and 2012 sample years. Artificial lakes are lakes, and process-based explorations of their behavior can help us better know management options.

Taken together, this dissertation examines an artificial version of each of the major aquatic ecosystem types: stream, wetland, and lake. It examines the processes controlling their ecological condition with increasing intricacy with each chapter, and finds ways that artificial aquatic ecosystems are both similar to and different from natural ones. This dissertation provides a new way of looking at the constraints and opportunities that artificial waterbodies afford those in charge of them and interested in their conservation potential.

Groundwater has an important role in forging the composition of surface water, supplying nutrients crucial for the development of balanced ecosystems and potentially introducing contaminants into otherwise pristine surface water. Due to water-rock interactions radium (Ra) in groundwater is typically much more abundant than in surface water. In saline environments Ra is soluble and is considered a conservative tracer (apart for radioactive decay) for Ra-rich groundwater seepage. Hence in coastal environments, where mostly fresh groundwater seep into saline surface water, Ra has been the prominent tracer for tracking and modeling groundwater seepage over more than three decades. However, due to its reactivity and non-conservative behavior, Ra is rarely used for tracing groundwater seepage into fresh or hypersaline surface water; in freshwater, Ra is lost mostly through adsorption onto sediments and suspended particles; in hypersaline environments Ra can be removed through co-precipitation, most notably with sulfate salts.

This work examines the use of Ra as a tracer for groundwater seepage into freshwater lakes and rivers and into hypersaline lakes. The study examines groundwater-surface water interactions in four different environments and salinity ranges that include (1) saline groundwater discharge into a fresh water lake (the Sea of Galilee, Israel); (2) modification of pore water transitioning from saline to freshwater along their flow through sediments (pore water in sediments underlying the Sea of Galilee, Israel); (3) fresh groundwater discharge into hypersaline lakes (Sand Hills, Nebraska); and (4) fresh groundwater discharge into a fresh water river (Neuse River, North Carolina). In addition to measurement of the four Ra isotopes (226Ra, 228Ra, 223Ra, 224Ra), this study integrates geochemical (major and trace elements) with additional isotopic tools (strontium and boron isotopes) to better understand the geochemistry associated with the seepage process. To better understand the critical role of salinity on Ra adsorption, this study includes a series of adsorption experiments. The results of these experiments show that Ra loss through adsorption decreases with increasing salinity, and diminishes in salinity as low as ~5% of the salinity of seawater.

Integration of the geochemical data with mass-balance models corrected for adsorption allows estimating groundwater seepage into the Sea of Galilee (Israel) and the Neuse River (North Carolina). A study of the pore water underlying the Sea of Galilee shows significant modifications to the geochemistry and Ra activity of the saline pore water percolating through the sediments underlying the lake. In high salinity environments such as the saline lakes of the Nebraska Sand Hills, Ra is shown to be removed through co-precipitation with sulfate minerals, its integration into barite (BaSO₄) is shown to be limited by the ratio of Ra:Ba in the precipitating barite.

Overall, this work demonstrates that Ra is a sensitive tracer for quantifying groundwater discharge even in low-saline environments. Yet the high reactivity of Ra (adsorption, co-precipitation, production of the short-lived isotopes) requires a deep understanding of the geochemical processes that shape and control Ra abundances in water resources.