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Wetland restoration has numerous potential ecological and societal benefits, one of which is the retention of phosphorus (P) and consequent protection of downstream water bodies from eutrophication. Past studies focused on influents to and effluents from a variety of wetland types have documented net P retention. However, some wetland systems are less effective at P capture and wetland P retention capacity can change over time. Certain wetland types - especially riparian wetlands restored on former agricultural land - remain understudied. In Vermont, most of the over 4000 potential wetland restoration sites in the Lake Champlain Basin are located on current or former agricultural fields, and little information is available to inform estimates of net P retention (i.e., P balances) for such sites. In this dissertation, I examined various factors affecting P balances in riparian wetlands restored on historically farmed soils of Vermont. P balance in a riparian wetland is largely a function of particulate P capture (e.g., deposition of particle-attached P during floods) and soluble reactive P (SRP) loss (e.g., release of SRP from soils). In Chapter 1, I determined the threshold in P saturation ratio (PSR) for riparian soils in Vermont, enabling calculation of a soil P storage capacity (SPSC) metric. I then quantified soil SRP release using intact soil core incubations with simulated floods for sites ranging from active farms to mature wetlands and confirmed that PSR, SPSC, and other soil parameters were strong predictors of SRP loss during inundation. In Chapter 2, I monitored P dynamics in soil, water, and vegetation at three restored riparian wetlands on former agricultural land in the Lake Champlain Basin, focusing on factors that affect P deposition and SRP release. At wetland sampling plots, observed inorganic sediment gain and decreased water column total suspended solids concentrations relative to the river/inflow indicated that wetlands were effectively trapping particles. Accretion of inorganic P (i.e., best estimate for mineral P deposited during floods) ranged from 0.1 to 1 g P m-2 yr-1 depending on site and elevation. Elevated SRP concentrations in wetland water columns relative to the river sources indicated internal SRP release from soils, and high frequency data indicated that factors such as temperature, dissolved oxygen, and primary production likely influence SRP dynamics. In Chapter 3, I developed a wetland P dynamics model that can generate estimates of net P retention from a simple set of soil and hydrologic inputs, considering both P deposition and SRP release. For proof of concept, I simulated the wetlands monitored in Chapter 2 using two years of monitoring data and a set of model scenarios. I found that net total P balance was typically positive (-0.04 to 0.24 g P m-2 yr-1), with average P retention efficiency of ~40%, though there was substantial variability depending on site and scenario. P retention efficiency was especially sensitive to changes in influent P and total suspended solids concentrations, with the greatest net P retention predicted for systems receiving influent floodwater with high P concentrations. Reduction of influent SRP concentrations promoted SRP release from soils, suggesting that legacy soil P in the wetlands might cause a time lag between the adoption of upstream best management practices and reduction in downstream SRP concentrations. In the future, the model developed in Chapter 3 can be applied more broadly to investigate the potential P retention benefits of wetland restoration at candidate sites across Vermont. Together, the information put forth by this dissertation provides a suite of data and tools that researchers and managers can use to enhance the P retention benefits of riparian wetland restoration.
The Clean Water Act (CWA) requires that wetlands be protected from degradation because of their important ecological functions including maintenance of high water quality and provision of fish and wildlife habitat. However, this protection generally does not encompass riparian areasâ€"the lands bordering rivers and lakesâ€"even though they often provide the same functions as wetlands. Growing recognition of the similarities in wetland and riparian area functioning and the differences in their legal protection led the NRC in 1999 to undertake a study of riparian areas, which has culminated in Riparian Areas: Functioning and Strategies for Management. The report is intended to heighten awareness of riparian areas commensurate with their ecological and societal values. The primary conclusion is that, because riparian areas perform a disproportionate number of biological and physical functions on a unit area basis, restoration of riparian functions along America's waterbodies should be a national goal.
Alteration of global nitrogen (N) and phosphorus (P) cycles to support livestock and crop production is the most significant driver of global nutrient surpluses. Losses of excess nutrients to the environment contribute to eutrophication of aquatic systems, leading to harmful algal blooms (HABs), hypoxia, and fish kills. Livestock and dairy production are directly linked to the acceleration of eutrophication via nutrient losses from animal manure. Lake Champlain has been experiencing HABs since the 1970s, and a total maximum daily load (TMDL) is in place to reduce P loading to the lake, with much of the reduction in P load being required to come from the agricultural sector. It is critical to understand nutrient movement and the impact of a changing regional climate in manure-based agricultural watersheds, as dairy farming is the primary agricultural sector in Vermont. Additionally, studying agricultural management practices to mitigate P losses is imperative to meet the target P load reductions set forth by the TMDL. The first portion of this thesis analyzes seasonal differences in nutrient movement in two manure-based agricultural watersheds in the Vermont Lake Champlain Basin (VT LCB) with varying extent of agricultural land use. The results show that the spring and summer had the smallest seasonal loads of total P (TP) and dissolved P (DP) in runoff. The smaller summer P loads appear to be related to periods of drought, while the smaller P loads in the spring are likely related to less manure P built up in the watershed that could be transported to surface waters. Approximately 40% of the cumulative TP load and 43% of the cumulative DP load was discharged from the watersheds in the fall. The increased fall TP and DP loads were likely due to the application of manure across the watersheds during this period. The data suggest that soil erosion is relatively less dominant as a driver of watershed P discharge during times when manure was available for transport post-application (e.g., fall and summer), and more closely linked to watershed P loss during times when less new manure was available (e.g., spring). The results suggest better management of manure application rates and timing as well as increased implementation of agricultural management practices are needed to address increased P transport throughout the year, and especially during the fall. The second portion of this thesis assesses the efficacy of edge-of-field (EOF) iron-based filters for P removal. In-field agricultural management practices such as no-till management and cover cropping target reductions in TP, but do not effectively address DP. EOF filters are a promising management practice for reducing DP losses. Storm runoff at the inlet and outlet of one subsurface and two surface EOF filters was monitored for 10 months. The subsurface filter proved very effective for soluble reactive P (SRP) and TP removal, removing 99% of cumulative SRP load and 91% of TP load from monitored events. The surface filters had varied results, with the east surface filter removing 19% of SRP load and 72% of TP load, and the west surface filter removing 52% of SRP load and having no effect on TP load. The findings highlight the importance of filter sizing and design to minimize the impact of sediment loading and preferential flow pathways on surface EOF filter performance. The study provides early evidence that tile drain filters are a highly effective management strategy for mitigating SRP and TP losses from agricultural fields.
Riparian wetlands are important areas for regulating phosphorus (P) transfer in shallow groundwater. Limited knowledge is currently available regarding the effects of hydrological regimes on the transfer process of various P forms in shallow groundwater in upland-riparian-stream continuums in agricultural areas. This study focuses on P transfer in shallow groundwater within and between the riparian zone and hyporheic zone in Spencer Creek, and considers the effects on P transfer caused by flooding from the drawdown of the upstream Valens Reservoir, Hamilton, southern Ontario.
Nonpoint source pollution by phosphorus and sediment is a wide-spread problem across the United States and specifically in Vermont and the Lake Champlain Basin. Best management of nonpoint source loading will likely involve a combination of land use and stream channel modifications, but few studies have comprehensively examined the relative importance of land use, streambank instability, and soil phosphorus. Thus, it is important to understand the associations between these characteristics, as well as their overall, relationship to watershed nutrient loading dynamics. The main objectives of this study were (1) to examine the impacts of land use at the watershed and near-stream scales on total suspended solids (TSS), total phosphorus (TP), and soluble reactive phosphorus (SRP), (2) to explore the links between geomorphic condition and phosphorus and sediment concentrations and loads throughout the watershed and at different spatial scales, and (3) to investigate the importance of soil phosphorus concentrations in stream banks in contributing to the overall phosphorus load. TP, SRP, and TSS samples were collected from eight sites located at tributary junctures and one site at the mouth of Hungerford Brook, a 50 km2 watershed in the Lake Champlain Basin, under storm and baseflow conditions. Rapid geomorphic assessment (RGA) scores, land use, and soil phosphorus concentrations were collected for reaches upstream of sampling locations. Both nested and unnested design multivariate modeling was used to evaluate the importance of characteristics in the individual subwatersheds (unnested) or the entire upstream watershed (nested). SRP, TP, and TSS were predicted as both concentrations and instantaneous loads, using raw quantifications of subwatershed characteristics as well as these same characteristics standardized by the area of agriculture in the subwatershed. Correlation coefficients and principal components analysis were used to select variables that were used in Akaike information criterion (AIC) model selection and stepwise regression. Unnested variables used were agriculture, agriculture in a streamside buffer, proportion of corn, slope, channel degradation, and soil phosphorus. For the nested design, agriculture, agriculture in the buffer, channel aggradation, RGA score, and soil phosphorus concentrations were used. Best fit models were selected based on AICc scores and overall model R2. n ANOVA was also performed on the percent difference between storm flow concentrations and average baseflow concentrations. Results indicate that phosphorus and sediment transport occurs mainly during storm events and concentrations greatly exceed state water quality standards. Concentrations of SRP and TP were significantly lower at the mouth of Hungerford Brook than in upstream subwatersheds, indicating that deposition and storage are occurring in this downstream part of the watershed. SRP concentrations appear to be best explained by agriculture in the riparian buffer, while TP and TSS are influenced by agricultural land use at multiple spatial scales. Agricultural land use was associated with increased stream instability. These findings suggest that additional phosphorus and sediment management, targeted at increasing stream stability and reducing impacts from agriculture, are needed in order to reduce the overall load traveling to Lake Champlain.
The globally important nature of wetland ecosystems has led to their increased protection and restoration as well as their use in engineered systems. Underpinning the beneficial functions of wetlands are a unique suite of physical, chemical, and biological processes that regulate elemental cycling in soils and the water column. This book provides an in-depth coverage of these wetland biogeochemical processes related to the cycling of macroelements including carbon, nitrogen, phosphorus, and sulfur, secondary and trace elements, and toxic organic compounds. In this synthesis, the authors combine more than 100 years of experience studying wetlands and biogeochemistry to look inside the black box of elemental transformations in wetland ecosystems. This new edition is updated throughout to include more topics and provide an integrated view of the coupled nature of biogeochemical cycles in wetland systems. The influence of the elemental cycles is discussed at a range of scales in the context of environmental change including climate, sea level rise, and water quality. Frequent examples of key methods and major case studies are also included to help the reader extend the basic theories for application in their own system. Some of the major topics discussed are: Flooded soil and sediment characteristics Aerobic-anaerobic interfaces Redox chemistry in flooded soil and sediment systems Anaerobic microbial metabolism Plant adaptations to reducing conditions Regulators of organic matter decomposition and accretion Major nutrient sources and sinks Greenhouse gas production and emission Elemental flux processes Remediation of contaminated soils and sediments Coupled C-N-P-S processes Consequences of environmental change in wetlands# The book provides the foundation for a basic understanding of key biogeochemical processes and its applications to solve real world problems. It is detailed, but also assists the reader with box inserts, artfully designed diagrams, and summary tables all supported by numerous current references. This book is an excellent resource for senior undergraduates and graduate students studying ecosystem biogeochemistry with a focus in wetlands and aquatic systems.
Aldo Leopold, father of the "land ethic," once said, "The time has come for science to busy itself with the earth itself. The first step is to reconstruct a sample of what we had to begin with." The concept he expressedâ€"restorationâ€"is defined in this comprehensive new volume that examines the prospects for repairing the damage society has done to the nation's aquatic resources: lakes, rivers and streams, and wetlands. Restoration of Aquatic Ecosystems outlines a national strategy for aquatic restoration, with practical recommendations, and features case studies of aquatic restoration activities around the country. The committee examines: Key concepts and techniques used in restoration. Common factors in successful restoration efforts. Threats to the health of the nation's aquatic ecosystems. Approaches to evaluation before, during, and after a restoration project. The emerging specialties of restoration and landscape ecology.
This is a preliminary evaluation of the status of the science of wetland creation and restoration in the United States. It contains a series of regional reviews. Each review summarizes wetland creation and restoration experiences in broadly defined wetland regions (e.g. Pacific coastal wetlands, wooded wetlands of the Southeast). It also includes a series of theme papers, covering a wide range of topics of general application to wetland creation and restoration (hydrology, management techniques, planning).
In 1997, New York City adopted a mammoth watershed agreement to protect its drinking water and avoid filtration of its large upstate surface water supply. Shortly thereafter, the NRC began an analysis of the agreement's scientific validity. The resulting book finds New York City's watershed agreement to be a good template for proactive watershed management that, if properly implemented, will maintain high water quality. However, it cautions that the agreement is not a guarantee of permanent filtration avoidance because of changing regulations, uncertainties regarding pollution sources, advances in treatment technologies, and natural variations in watershed conditions. The book recommends that New York City place its highest priority on pathogenic microorganisms in the watershed and direct its resources toward improving methods for detecting pathogens, understanding pathogen transport and fate, and demonstrating that best management practices will remove pathogens. Other recommendations, which are broadly applicable to surface water supplies across the country, target buffer zones, stormwater management, water quality monitoring, and effluent trading.