Michael F. Walter

A GIS-based variable source area hydrology model

Effective control of nonpoint source pollution from contaminants transported by runoff requires information about the source areas of surface runoff. Variable source hydrology is widely recognized by hydrologists, yet few methods exist for identifying the saturated areas that generate most runoff in humid regions. The Soil Moisture Routing model is a daily water balance model that simulates the hydrology for watersheds with shallow sloping soils. The model combines elevation, soil, and land use data within the geographic information system GRASS, and predicts the spatial distribution of soil moisture, evapotranspiration, saturation-excess overland flow (i.e., surface runoff), and interflow throughout a watershed. The model was applied to a 170 hectare watershed in the Catskills region of New York State and observed stream flow hydrographs and soil moisture measurements were compared to model predictions. Stream flow prediction during non-winter periods generally agreed with measured flow resulting in an average r2 of 0·73, a standard error of 0·01 m3/s, and an average Nash-Sutcliffe efficiency R2 of 0·62. Soil moisture predictions showed trends similar to observations with errors on the order of the standard error of measurements. The model results were most accurate for non-winter conditions. The model is currently used for making management decisions for reducing non-point source pollution from manure spread fields in the Catskill watersheds which supply New York Citys drinking water. Copyright

Phosphorus transport into subsurface drains by macropores after manure applications: Implications for best manure management practices

Land application of liquid manure can result in nutrient enrichment of subsurface drainage effluent when conditions promote leaching or macropore flow. This contamination is most likely to occur when precipitation follows manure application closely and may cause environmental impacts to receiving waters. Field and column studies were initiated in New York to investigate the impact of manure applications on phosphorus (P) transport through the soil into subsurface drains. Field studies evaluated tile effluent contamination from liquid manure under wet and dry antecedent soil moisture conditions (year 1) and under disk and plow tillage practices (year 2). In year 1, liquid dairy manure was broadcast on the surface and the field was then irrigated. Though the tile drains in the wet plots flowed much earlier and in greater volume than the drains in the dry plots, both wet and dry plots produced similar average peak total phosphorus (TP) concentrations. Irrigation 6 days later produced similar tile discharges, but the peak TP concentrations were about one-third of the earlier values. Cumulative TP loss was significantly higher from wet than dry plots. In year 2, manure was tilled into the soil via one-pass disking or plowing before irrigation commenced. The disking did not incorporate the manure into the soil as effectively as did plowing and exhibited one order of magnitude higher effluent TP concentrations and cumulative TP loss. The timing of P transport in tile effluent relative to the tile flow is consistent with macropore transport as the primary mechanism moving TP through the soil. Column studies utilizing packed soil and artificial macropores were used to examine further the role of macropore size on P sorption to pore walls. Dissolved P was added directly to the macropore, and the effluent from the macropore showed that soluble P may be transported through macropores 1 mm or greater with negligible P sorption to pore walls. In the absence of macropores, no measurable P was transported through the soil columns. Consequently, high P concentrations observed in the tile drain effluent soon after manure application during the field studies can be attributed to macropore transport processes. Even small continuous macropores are potential pathways. Plowing-in manure apparently disturbs these macropores and promotes matrix flow, resulting in greatly reduced P concentrations in the drainage effluent.

Closed Form Solution for Pesticide Loss in Runoff Water

ABSTRACT PESTICIDE use in agriculture has undoubtedly bene-fited crop production efficiency. Its convenience and cost effectiveness have greatly simplified the task of pest control for the farmer, and at the same time have confer-red on consumers the benefit of relatively inexpensive agricultural goods. However, chemical control of agricultural pests has also created numerous ecological problems, problems which are in part caused by the tendency of applied pesticides to migrate away from target fields via runoff and erosion to surrounding sur-face waters. Modeling of pesticide loss in runoff water has been at-tempted by Crawford and Donigian, 1973; Frere et al., 1975; Donigian et al., 1976, 1977; Adams and Kurisu, 1976; McElroy et al., 1976. All but the latter group have developed continuous simulation models that are capable of modeling losses of pesticides that are in-termediate and strongly adsorbed to soil. McElroy et al, 1976, have developed a simple loading formula that only applies to strongly adsorbed pesticides. No one, to our knowledge, has developed a simple procedure for model-ing intermediately adsorbed pesticide loss in the runoff water. The objective of our research was to develop a simple model which would be used to predict runoff losses of pesticides from agricultural lands. Once developed, this model would then enable us to determine the possible ef-fects of best management practices on the volume of pesticides transported via runoff from application sites to surface waters.

Application of SMR to modeling watersheds in the Catskill Mountains

Very few hydrological models commonly used in watershed management are appropriate for simulating the saturation excess runoff. The Soil Moisture Routing model (SMR) was developed specifically to predict saturation excess runoff from variable source areas, especially for areas where shallow interflow controls saturation. A recent version of SMR was applied to two rural catchments in the Catskill Mountains to evaluate its ability to simulate the hydrology of these systems. Only readily available meteorological, topographical, and landuse information from published literature and governmental agencies was used. Measured and predicted streamflows showed relatively good agreement; the average Nash–Sutcliffe efficiency for the two watersheds were R2=72% and R2=63%. Distributed soil moisture contents and the locations of hydrologically sensitive areas were also predicted well.

Runoff responses among common land uses in the uplands of Matalom, Leyte, Philippines

Changing tropical hydrologic regimes have been attributed to conversion from tropical forest to agricultural use and are a threat to many tropical upland ecosystems. A series of experiments were conducted in headwater catchments of Matalom, Leyte, Philippines, to quantify the effect on the near-surface hydrology of land uses common to the steep slopes and thin, calcareous soils. Overland and subsurface runoff were collected to compare the surface hydrologic response of forested, tilled, slash/mulch, and pasture catchments. The forest site demonstrated the lowest annual runoff response, at less than 3% of rainfall, and the highest rainfall threshold which initiated runoff. Conversely, the pasture site demonstrated the greatest annual runoff response (76%) with the lowest thresholds. A pasture with contour-hedgerows demonstrated greater infiltration than the pasture without this conservation practice, generating runoff at 31% of annual rainfall. The plowed and slash/mulch sites had similar annual runoff responses, at 17% and 13% of rainfall, although the predominant flow pathway differed between these sites. Surface runoff accounted for the majority of runoff at the plowed and pasture-fallow sites; whereas, interflow provided the largest contribution to runoff at the slash/mulch and forest sites.

WATER QUALITY IMPACTS OF TILE DRAINS IN SHALLOW, SLOPING, STRUCTURED SOILS AS AFFECTED BY MANURE APPLICATION

Tile drains are one of several best management practices whose purpose is to reduce the export of contaminants to receiving waters. It is conventionally assumed that contaminants are effectively retained in the soil prior to subsurface water entering the drain. Two conditions may result in significantly elevated contaminant loading in tile effluent: preferential flow through macropores, and steep slopes which increase drainage in shallow, permeable soils on a hardpan. This article presents field monitoring data on phosphorus and fecal coliforms measured in New York State watersheds under both conditions described, and examines the mechanisms for increased tile drain contaminant delivery from manure-applied fields to streams. Soluble phosphorus concentrations peaked at 1.17 mg/L, and as much as 37% of soluble phosphorus was exported from the field site via subsurface drains. Fecal coliform concentrations peaked at 71,000 organisms/100 mL. The total number of fecal coliforms discharged from the drain during the flow event would have required about 75 fold dilution to bring the fecal coliform concentration to a municipal wastewater treatment plant discharge effluent standard of 400 organisms/100 mL. Under some conditions, the contaminant discharge from subsurface drains may also have significant water quality impacts to receiving waters.

Nonpoint Source Pollution Control by Soil and Water Conservation Practices

ABSTRACT THERE has been a tendency to equate best manage-ment practices, as defined in water quality legisla-tion, with soil and water conservation practices. The effectiveness of SWCPs at controlling potential pollut-ants other than sediment depends on the characteristics of pollutants. Pollutants have been categorized in groups having distinctly different soil adsorption properties which have been related to the effect of SWCPs on water and soil movement.

Residual phosphorus in runoff from successional forest on abandoned agricultural land: 1. Biogeochemical and hydrological processes

Soluble reactive phosphorus (SRP)concentrations measured in runoff fromabandoned agricultural land now in forestsuccession in the northeastern United Stateswere significantly higher than expected fromundisturbed forest land. This finding differsfrom P uptake in hardwood forest successionfollowing natural disturbance. Fieldmonitoring of a 16.6 ha old-field regrowthforest stand in the Catskills Mountains, NewYork, USA demonstrated runoff SRP trendsincluding an early summer flush that could notbe explained by simple dilution. An assay ofoutflow sediment and biomass, flowpath sedimentand biomass, forest floor leaf litter andbiomass, and Bh horizon mineral soil indicatedthat surface litter from the regrowth forestprovided the most significant contribution tothe elevated SRP in runoff. It is posited thatmicrobial mineralization of residual organic Pin surface litter coupled with the transientprocess of SRP mobilization at the soil surfaceresulting from a rising saturated layerfollowed by dissolution in surface runoff mayelevate SRP to the range observed. MeasuredSRP concentrations remain lower than reportedvalues for crop or pastureland. The resultsreported represent an important deviation fromthe prevailing view that forest land does notcontribute to eutrophication (based on enhancedP uptake in forest succession); this is aconsequence of residual P from landabandonment – a widespread practice throughoutthe northeastern US and other regions.

PROCESSES OF SOIL MOVEMENT ON STEEP CULTIVATED HILL SLOPES IN THE VENEZUELAN ANDES

Abstract Erosion from cultivated lands continues to threaten the sustainability of commercial and subsistence agriculture around the world. Although most erosion is attributed to rainfall-induced runoff, other processes were observed which may account for a large portion of soil movement on sloping farm lands. Soil movement was measured on 15 parcels cultivated by subsistence farmers in the Venezuelan Andes as part of a broader study on adoption of soil conservation practices. Sediment traps were installed at the outlet of fields with slopes ranging from 33% to 78%. Based on the type of material found in the traps—clods, stones and some consolidated earth-soil movement was attributed to plowing, weeding, concentrated flows entering the field from above and, to a lesser extent, rainfall. Soil flux ranged from 1.5 to 58.7 kg m−1 yr−1 with an average of 31.1 kg m−1 yr−1. Three parcels underwent low flux, 1.5 to 5.7 kg m−1 yr−1 and 12 showed a higher flux, 16.7 to 58.7 kg m−1 yr−1. This study served to identify a number of soil erosion mechanisms not often considered when designing soil conservation programs targeted for areas with steep slopes. Tillage translocation and weeding within parcels contributed considerably more to soil and stone movement than did rainfall. The findings suggest that, when designing soil conservation programs for such areas, emphasis should be placed on methods devised to minimize soil disturbance. Among the practices that may be promoted are minimum or zero-tillage, the use of ground covers to control weeds and the installation of stone or grass barriers to retard the downward movement of soil.

The effect of allocation schedules on the performance of irrigation systems with different levels of spatial diversity and temporal variability

Abstract This paper quantitatively examines the effect of spatial diversity and temporal variability on the performance of an irrigation system. The Irrigation Land Management (ILM) computer model was used to simulate over a 20-year period the response of four test systems constructed with different levels of spatial diversity and temporal variability to three schedules representing different levels of management flexibility. From the simulation runs it is apparent that the need for more flexible schedules becomes greater as the irrigation system becomes more spatially diverse and its climate becomes more variable. Choosing the right schedules depends not on maximizing production, but rather on optimizing production given the costs of management and the context within which the system operates.