R. D. Harmel

PRACTICAL GUIDANCE FOR DISCHARGE AND WATER QUALITY DATA COLLECTION ON SMALL WATERSHEDS

Many sampling projects have been initiated or modified in recent years to quantify the effects of water quality protection and enhancement programs. Although comprehensive references on the theory and procedures related to discharge data collection have been published, similar guides to water quality sampling are not available. Several sources provide general guidance on sampling project design and on manual sampling procedures, but only recently has detailed information on automated storm water quality sampling been developed. As a result, a compilation of available information on the design of water quality sampling projects is needed to support sound decision-making regarding data collection resources and procedural alternatives. Thus, the objective of this article is to compile and present practical guidance for collection of discharge and water quality constituent data at the field and small watershed scale. The guidelines included are meant to increase the likelihood of project success, specifically accurate characterization of water quality within project resource constraints. Although many considerations are involved in establishing a successful sampling project, the following recommendations are generally applicable to field and small watershed studies: (1) consider wet-weather access, travel time, equipment costs, and sample collection method in the selection of sampling site numbers and locations; (2) commit adequate resources for equipment maintenance and repair; (3) assemble a well-trained, on-call field staff able to make frequent site visits; (4) establish reliable stage-discharge relationships for accurate discharge measurement; (5) use periodic manual grab sample collection with adequate frequency to characterize baseflow water quality; (6) use flow-interval or time-interval storm sampling with adequate frequency to characterize storm water quality; and (7) use composite sampling to manage sample numbers without substantial increases in uncertainty.

Nitrogen and phosphorus runoff from cropland and pasture fields fertilized with poultry litter

Application of litter and other organic by-products to agricultural land off site of animal production facilities has created both environmental concerns and agro-economic opportunities, but limited long-term, field-scale data are available to guide management decisions. Thus, the objective of this study was to determine the water quality effects of repeated annual poultry litter application as a cropland and pasture fertilizer. Eight years of data collected on ten field-scale watersheds indicated several significant water quality differences based on litter rate (0.0 to 13.4 Mg ha−1 [0 to 6 ton ac−1]) and land use (cropland and pasture). On cropland fields, increasing litter rates (with corresponding decreases in supplemental inorganic nitrogen [N]) increased runoff orthophosphate phosphorus (PO4-P) concentrations but reduced extreme high nitrate nitrogen (NO3-N) concentrations. Whereas runoff PO4-P concentrations were somewhat similar between land uses, NO3-N concentrations were much lower in pasture runoff because of supplemental inorganic N application, reduced nutrient uptake potential, and faster litter mineralization on cropland. Although considerable variability was observed, intra-annual runoff NO3-N and PO4-P concentrations generally exhibited curvilinear decay based on time since fertilizer application. In spite of repeated annual litter application and buildup of soil phosphorus (P) at high litter rates, few long-term trends in N and P runoff were evident due to the dynamic interaction between transport and source factors. These results support several practical implications, specifically: (1) combining organic and inorganic nutrient sources can be environmentally friendly and economically sound if application rates are carefully managed; (2) high runoff N and P concentrations can occur from well-managed fields, which presents difficulty in regulating edge-of-field water quality; and (3) change in the animal industry mindset to view by-products as marketable resources could mitigate environmental problems, provide alternative fertilizer sources, and enhance animal industry revenue opportunities.

Assessing edge-of-field nutrient runoff from agricultural lands in the United States: How clean is clean enough?

Excess nutrient loading from numerous sources (e.g., agricultural and urban runoff, treatment plant discharge, and streambank erosion) continues to adversely impact water resources, and determination of the cause(s) of accelerated nutrient enrichment has become a contentious and litigious issue in several US regions. This paper addresses one fundamental question: What are acceptable levels of nutrients in runoff from agricultural fields? It focuses on the field scale where farmers and ranchers make management decisions. Not answering this question limits the effectiveness of on-farm management and policy alternatives to address agricultures contribution. To answer the question, some might suggest “direct comparison” with reference site data, existing criteria/standards, or measured data compilations. Alternatively, “indirect assessments” using soil test phosphorus (P) levels, P indices, field-scale models, or certainty programs might be suggested. Thus, to provide a scientific basis for policy debate and management decisions related to nutrient runoff from agricultural fields, we evaluated “direct comparisons” with measured data from case studies and evaluated “indirect assessment” alternatives. While acknowledging that scientific challenges and practical realities exist for each alternative, we concluded that certainty programs offer the most promise for ensuring acceptable nutrient runoff, and that field-scale models linked with watershed decision support tools are the most promising for assessing impacts on downstream water quality. Recognizing the reality that some nutrient loss is unavoidable from natural and anthropogenic sources, agriculture, industry, and municipalities are each encouraged to commit to implementing enhanced management where needed to minimize their sectors contribution to excess nutrients in our nations waters.

Measuring edge-of-field water quality: Where we have been and the path forward

Heightened pressure to demonstrate the resource benefits of conservation practices and continued high-profile water quality impairments and concerns are increasing the need to quantify edge-of-field (EOF) water quality. With this in mind, this manuscript summarizes previous developments in EOF water quality sampling and presents current research and glimpses into the future. This manuscript focuses on constituent sampling at the field-scale or at the “edge-of-field;” however, many of the findings are also applicable for small stream or small watershed sampling. With development of programmable automated samplers and initiation of numerous automated sampling projects, it became readily apparent that neither equipment manufacturers nor researchers could provide guidance on design components (e.g., sample initiation, timing/intervals, and type). This was problematic as available monitoring resources are too limited and data needs too great for such projects to be designed solely based on field experience and without a scientific basis or with complete disregard for potential data quality implications. Thus practical, science-based guidance for EOF sampling was developed and fundamental understanding of the inherent uncertainty was established to assist researchers, municipalities, consulting firms, and regulatory agencies improve data quality and monitoring resource efficiency. Looking to the future, further improvements are needed related to lower cost systems, practical improvements, and enhanced in situ sampling, along with enhanced understanding and consideration of data uncertainty in modeling and decision making.