Anthony T. O'Geen

Chapter one. Mitigating nonpoint source pollution in agriculture with constructed and restored wetlands.

Abstract Nonpoint source pollution (NPSP) from agricultural runoff threatens drinking water quality, aquatic habitats, and a variety of other beneficial uses of water resources. Agricultural runoff often contains a suite of water-quality contaminants, such as nutrients, pesticides, pathogens, sediment, salts, trace metals, and substances, contributing to biological oxygen demand. Increasingly, growers who discharge agricultural runoff must comply with water-quality regulations and implement management practices to reduce NPSP. Constructed and restored wetlands are one of many best management practices that growers can employ to address this problem. This review focuses on the ability of constructed and restored wetlands to mitigate a variety of water-quality contaminants common to most agricultural landscapes. We found that constructed and restored wetlands remove or retain many water-quality contaminants in agricultural runoff if carefully designed and managed. Contaminant removal efficiency generally exceeded 50% for sediment, nitrate, microbial pathogens, particulate phosphorus, hydrophobic pesticides, and selected trace elements when wetlands were placed in the correct settings. There are some potentially adverse effects of constructed and restored wetlands that must be considered, including accumulation of mercury and selenium, increased salinity, mosquito habitat, and greenhouse gas emissions. Proper wetland management and design features are discussed in order to reduce these adverse effects, while optimizing contaminant removal.

Bioavailability and fate of phosphorus in constructed wetlands receiving agricultural runoff in the San Joaquin Valley, California.

Elevated nutrient concentrations in agricultural runoff contribute to seasonal eutrophication and hypoxia in the lower portion of the San Joaquin River, California. Interception and filtration of agricultural runoff by constructed wetlands may improve water quality of return flows ultimately destined for major water bodies. This study evaluated the efficacy of two small flow-through wetlands (2.3 and 7.3 ha; hydraulic residence time = 11 and 31 h) for attenuating various forms of P from irrigation tailwaters during the 2005 irrigation season (May to September). Our goal was to examine transformations and removal efficiencies for bioavailable P in constructed wetlands. Inflow and outflow water volumes were monitored continuously and weekly water samples were collected to measure total P (TP), dissolved-reactive P (DRP), and bioavailable P (BAP). Suspended sediment was characterized and fractionated into five operationally-defined P fractions (i.e., NH4Cl, bicarbonate-dithionite, NaOH, HCl, residual) to evaluate particulate P (PP) transformations. DRP was the major source of BAP with the particulate fraction contributing from 11 to 26%. On a seasonal basis, wetlands removed 55 to 65% of PP, 61 to 63% of DRP, 57 to 62% of BAP, and 88 to 91% of TSS. Sequential fractionation indicated that the bioavailable fraction of PP was largely associated with clay-sized particles that remain in suspension, while less labile P forms preferentially settle with coarser sediment. Thus, removal of potentially bioavailable PP is dependent on factors that promote particle settling and allow for the removal of colloids. This study suggests that treatment of tailwaters in small, flow-through wetlands can effectively remove BAP. Wetland design and management strategies that enhance sedimentation of colloids can improve BAP retention efficiency.

Litter contributions to dissolved organic matter and disinfection byproduct precursors in California oak woodland watersheds.

Export of dissolved organic matter (DOM) from California oak woodland ecosystems is of a great concern because DOM is a precursor for carcinogenic disinfection byproducts (DBPs) formed during drinking water treatment. Fresh litter and decomposed duff materials for the four dominant vegetation components of California oak woodlands: blue oak (Quercus douglassi H. & A.), live oak (Quercus wislizenii A. DC.), foothill pine (Pinus sabiniana Dougl.), and annual grasses, were exposed in natural condition for an entire rainy season (December to May) to evaluate their contributions of particulate (POC) and dissolved (DOC) organic carbon, particulate (PON) and dissolved (DON) organic nitrogen, inorganic nitrogen (NH4+ and NO3-), and trihalomethane (THM) and haloacetonitrile (HAN) formation potentials, to surface waters. Litter and duff materials can be significant sources of DOC (litter=29-126 mg DOC g(-1) C; duff=6.5-37 mg DOC g(-1) C) and THMs and HANs (up to 4600 mg-THMs g-C(-1) and 137 microg-HANs g-C(-1)). Blue oak litter had the highest yield of DOC, THM, and HAN precursors. When scaled to the entire watershed, leachate production yielded 445 kg-DOC ha(-1), as compared to DOC export via streams of 5.25 kg-DOC ha(-1). DOC transport to surface waters is facilitated by subsurface lateral flow through A horizons during storm events. The majority of DOM and DBP precursors was leached from plant materials in the initial rainfall events and thus may explain the seasonal stream pattern of a DOC pulse early in the rainy season.

Reactivity of litter leachates from California oak woodlands in the formation of disinfection by-products.

Litter materials from forested watersheds can be a significant source of dissolved organic matter (DOM) to surface waters that can contribute to the formation of carcinogenic disinfection by-products (DBPs) during drinking-water chlorination. This study characterized the reactivity of DOM from litter leachates of representative vegetation in oak woodlands, a major plant community in the Foothill Region of California. Leachates from fresh and decomposed litter (duff) from two oak species, pine, and annual grasses were collected for an entire rainy season to evaluate their reactivity to form DBPs on chlorination. Relationships among specific ultraviolet absorbance (SΔUVA), fluorescence index (FI), specific differential ultraviolet absorbance (SΔUVA), specific chlorine demand (SCD), and the dissolved organic carbon:dissolved organic nitrogen (DOC:DON) ratio to the specific DBP formation potential (SDBP-FP) were examined. The DOM derived from litter materials had considerable reactivity in forming trihalomethanes (THMs) (1.80-3.49 mmol mol), haloacetic acid (HAAs) (1.62-2.76 mmol mol(-1)), haloacetonitriles (HANs) (0.12-0.37 mmol mol(-1)), and chloral hydrate (CHD) (0.16-0.28 mmol mol). These values are comparable to other identified watershed sources of DBP precursors reported for the California Delta, such as wetlands and organic soils. Vegetation type and litter decomposition stage (fresh litter versus 1-5 yr-old duff) were key factors that determined characteristics of DOM and their reactivity to form DBPs. Pine litter had significantly lower specific THM formation potential compared with oak and grass, and decomposed duff had a greater DON content, which is a precursor of HANs and other nitrogenous DBPs. The SΔUVA and SDBP-FP were temporally variable and dependent on vegetation type, degree of decomposition, and environmental conditions. Among the optical properties of DOM, SΔUVA was the only parameter that was consistently correlated with SDBP-FP.

DEVELOPMENT OF A GIS DATABASE FOR GROUND-WATER RECHARGE ASSESSMENT OF THE PALOUSE BASIN

The advent of Geographic Information Systems (GIS) is bringing about the expansion of soil survey data into interdisciplinary research projects. A GIS database was developed for the Palouse Basin in northern Idaho and eastern Washington to identify areas where soil and geologic features are likely to impact ground-water recharge. Using GeoProcessing operations in ArcView, 1:24,000 soil survey data and surficial geology were combined. The resulting ArcView-based GIS coverage was used to delineate recharge mechanisms and classify recharge potential in the Palouse Basin. A database was developed using binary weighting and index overlay modeling methods to assign values to soil map units based on selected soil characteristics, including permeability rates, depth to bedrock, and the presence of perched water tables. These data were then linked to Basin recharge mechanisms to produce maps indicating the potential for deep percolation through soil and subsequent recharge to the local aquifer system. Results indicate that recharge through loess is the most spatially extensive recharge mechanism, operating over 71% of the total study area. Of this, approximately 2300 ha have high potential for recharge. Recharge through stream loss operates over 16% of the total study area, whereas percolation through localized fractures in bedrock is the least extensive recharge mechanism, operating over just 13% of the total study area. Although stream loss and infiltration along Basin margins occupy a limited spatial extent they have more land area rated as ‘high potential’ for recharge. There is lower recharge potential in the eastern portion of the Basin because of the presence of extensive hydraulically restrictive subsoil horizons.

Hydrologic processes in valley soilscapes of the eastern Palouse basin in northern Idaho

Vadose zone hydrology in the eastern Palouse Basin of northern Idaho is poorly understood because loess deposits often contain multiple hydraulically restrictive horizons that impede water flow. Valley soilscapes are of particular interest from a hydrologic perspective, because during the winter months, most of the precipitation is redistributed as runoff and throughflow into these landscape positions. Understanding the relationship between near-surface perched water table dynamics and vadose zone hydraulic processes in valley soilscapes is necessary to assess the sustainability of the groundwater resource. We implemented a combined approach to assess hydrologic processes in valley positions using hydrometric measurements, natural tracers, and stratigraphic observations. Hydrographs of near-surface monitoring wells indicate that valley positions maintain a thicker zone of saturation for longer duration compared with adjacent upland positions. Deep tensiometers demonstrate that multiple zones of seasonal saturation develop within the vadose zone of valley soilscapes in response to paleosol fragipan horizons and sediments of contrasting hydraulic conductivity. In some instances, the saturated thickness of vadose zone water tables was greater than 2.0 m and, because they are confined, displayed a positive pressure head. On adjacent uplands, seasonal saturation occurs only above the uppermost fragipan. Eluvial horizons having low Mnd correspond to zones of saturation, whereas aquitards reflect Mnd maxima. The recharge rate calculated using natural Cl− mass balance was 2.4 mm y−1 and did not correspond to measurements of saturated thickness by tensiometers. In addition, natural chloride profiles of other valley soilscapes display differences in recharge rates according to regional patterns in soil development. Together, deep tensiometer readings, secondary Mn distributions, and Cl− profiles suggest that groundwater recharge does not occur via piston flow. Detailed stratigraphic analysis illustrates that preferential flow is a possible recharge mechanism. Results suggest that valley soilscapes play an important role in both surficial and deep regolith hydrological processes in the Palouse Basin.

The Genesis and Exodus of Vascular Plant DOM from an Oak Woodland Landscape

Evaluating the collective impact of small source inputs to larger rivers is a constant challenge in riverine biogeochemistry. In this study, we investigated the generation of dissolved organic matter (DOM) in a small oak woodland catchment in the foothills of northern California, the subsequent transformation in lignin biomarkers and chromophoric DOM (CDOM) parameters during transport through the landscape to an exporting stream, and finally the overall compositional impact on the larger receiving stream and river. Our study included a natural leaching experiment in which precipitation passing through oak, pine, and grass litter and duff samples was collected after each of a series of storms. Also included were soil trench samples to capture subsurface flow, stream samples along with point-source reservoir inputs, and samples of canopy throughfall, stemflow, and gopher hole (bypass) flow. The litter/duff leaching study demonstrated changing DOM fractionation patterns throughout the season, as evidenced by changing lignin compositions in the leachates with each successive storm. This adds a necessary seasonal component to interpreting lignin compositions in streams, as the source signatures are constantly changing. Released DOM from leaching was modified extensively during transit through the subsurface to the stream, with preferential increases in aromaticity as evidenced by increases in carbon-normalized absorbance at 254 nm, yet preferential decreases in lignin phenols, as evidence by carbon-normalized lignin yields in the headwater stream that was less than half that of the litter/duff leachates. Our extensive number of lignin measurements for source materials reveals a much more complex perspective on using lignin as a source indicator, as many riverine values for syringyl:vanillyl and cinnamyl:vanillyl ratios that have previously been interpreted as degraded lignin signatures are also possible as unmodified source signatures. Finally, this study demonstrated that the impact of numerous small headwater streams can significantly overprint the DOM signatures of much larger rivers over relatively short distances spanning several to tens of kilometers. This finding in particular challenges the assumption that river studies can be adequately conducted by focusing only on the main tributaries.

Montane meadow hydropedology, plant community, and herbivore dynamics

Montane meadows provide multiple ecological and economic benefits, and are widely considered areas of high conservation value. There is growing interest in balancing multiple land-uses on these and other focal working landscapes to provide for economic, social, and conservation goals. Globally, livestock grazing has been used as a management and conservation tool in many ecosystems; however, there is substantial concern—particularly for montane meadows—that grazing negatively impacts ecosystem functions and services. The mechanisms by which excessive livestock grazing can degrade meadow function have been well documented; yet, for hydrologically functional meadow systems, we know little about meadow-scale linkages in the hydrologic-soil-plant-grazing animal continuum, which limits our ability to develop riparian grazing conservation strategies. We conducted a cross-sectional, observational survey of hydrology, soils, plant communities, and cattle forage resource use across 24 functional montane meadows of the central Sierra Nevada Mountain Range in California, USA. By linking principles of plant community ecology and foraging theory, we were able to unravel relationships and drivers between hydropedologic conditions, plant community characteristics, and cattle grazing patterns. Our work demonstrates that hydrology is a critical driving factor of cattle foraging response, plant community attributes, and soil properties across these wetland ecosystems. Results indicate that these systems are resilient to the observed gradient of grazing disturbances. This information advances our understanding of how meadow-scale heterogeneity can be utilized in managing for multiple, and potentially conflicting, ecosystem services across working landscapes—particularly in the face of projected future climate changes and continually limited resources to support conservation and restoration projects.

Food, water, and fault lines: Remote sensing opportunities for earthquake-response management of agricultural water.

Earthquakes often cause destructive and unpredictable changes that can affect local hydrology (e.g. groundwater elevation or reduction) and thus disrupt land uses and human activities. Prolific agricultural regions overlie seismically active areas, emphasizing the importance to improve our understanding and monitoring of hydrologic and agricultural systems following a seismic event. A thorough data collection is necessary for adequate post-earthquake crop management response; however, the large spatial extent of earthquakes impact makes challenging the collection of robust data sets for identifying locations and magnitude of these impacts. Observing hydrologic responses to earthquakes is not a novel concept, yet there is a lack of methods and tools for assessing earthquakes impacts upon the regional hydrology and agricultural systems. The objective of this paper is to describe how remote sensing imagery, methods and tools allow detecting crop responses and damage incurred after earthquakes because a change in the regional hydrology. Many remote sensing datasets are long archived with extensive coverage and with well-documented methods to assess plant-water relations. We thus connect remote sensing of plant water relations to its utility in agriculture using a post-earthquake agrohydrologic remote sensing (PEARS) framework; specifically in agro-hydrologic relationships associated with recent earthquake events that will lead to improved water management.