EFFECT OF WATERSHED SUBDIVISION ON SWAT FLOW,SEDIMENT, AND NUTRIENT PREDICTIONS1

ABSTRACT: The size, scale, and number of subwatersheds can affect a watershed modeling process and subsequent results. The objective of this study was to determine the appropriate level of subwatershed division for simulating flow, sediment, and nutrients over 30 years for four Iowa watersheds ranging in size from 2,000 to 18,000 km² with the Soil and Water Assessment Tool (SWAT) model. The results of the analysis indicated that variation in the total number of subwatersheds had very little effect on streamflow. However, the opposite result was found for sediment, nitrate, and inorganic P; the optimal threshold subwatershed sizes, relative to the total drainage area for each watershed, required to adequately predict these three indicators were found to be around 3, 2, and 5 percent, respectively. Decreasing the size of the subwatersheds below these threshold levels does not significantly affect the predicted levels of these environmental indicators. These threshold subwatershed sizes can be used to optimize input data preparation requirements for SWAT analyses of other watersheds, especially those within a similar size range. The fact that different thresholds emerged for the different indicators also indicates the need for SWAT users to assess which indicators should have the highest priority in their analyses.     

Geolocation of free-ranging fish on the European continental shelf as determined from environmental variables

Demersal fish cannot readily be tracked using satellite-based or light-based geolocation techniques. As an alternative, we describe the tidal location method, which uses tidal data recorded by electronic data storage tags (DSTs), to determine geoposition. Times of high water (H) and tidal ranges (R) recorded by DSTs moored at known locations, and from free-swimming tagged plaice, Pleuronectes platessa, were compared with a North Sea tidal database to identify all positions with matching values of H and R. Within the recording precision of the tag (ǂ.2 m, ᆞ min) and the predicted accuracy of the model generated tidal data (ǂ.15 m, ᆨ min), geolocations over much of the North Sea and eastern English Channel were predicted to be accurate to within 40 km, sometimes to within 10 km. Positional estimates of the moored tags were within 15.7Dž.5 km of the actual locations. Geolocations made from tagged plaice within 5 days of release and 5 days pre-recapture were within 35ᆬ km and 37ᆫ km of release and recapture positions respectively. Our results demonstrate the ability of this method to accurately describe the migrations of North Sea plaice throughout their geographical range with a level of accuracy unattainable using light-based geolocation. The method could equally be applied to any shelf-dwelling demersal fish that periodically rests on the sea-bed for the duration of a tidal cycle. In fisheries management, the method has clear potential application in defining the movements and migrations of other commercial species.     

LARGE AREA HYDROLOGIC MODELING AND ASSESSMENT PART II: MODEL APPLICATION1

ABSTRACT: This paper describes the application of a river basin scale hydrologic model (described in Part I) to Richland and Chambers Creeks watershed (RC watershed) in upper Trinity River basin in Texas. The inputs to the model were accumulated from hydro-graphic and geographic databases and maps using a raster-based GIS. Available weather data from 12 weather stations in and around the watershed and stream flow data from two USGS stream gauge station for the period 1965 to 1984 were used in the flow calibration and validation. Sediment calibration was carried out for the period 1988 through 1994 using the 1994 sediment survey data from the Richland-Chambers lake. Sediment validation was conducted on a subwatershed (Mill Creek watershed) situated on Chambers Creek of the RC watershed. The model was evaluated by well established statistical and visual methods and was found to explain at least 84 percent and 65 percent of the variability in the observed stream flow data for the calibration and validation periods, respectively. In addition, the model predicted the accumulated sediment load within 2 percent and 9 percent from the observed data for the RC watershed and Mill Creek watershed, respectively.     

LARGE AREA HYDROLOGIC MODELING AND ASSESSMENT PART I: MODEL DEVELOPMENT1

ABSTRACT: A conceptual, continuous time model called SWAT (Soil and Water Assessment Tool) was developed to assist water resource managers in assessing the impact of management on water supplies and nonpoint source pollution in watersheds and large river basins. The model is currently being utilized in several large area projects by EPA, NOAA, NRCS and others to estimate the off-site impacts of climate and management on water use, non-point source loadings, and pesticide contamination. Model development, operation, limitations, and assumptions are discussed and components of the model are described. In Part II, a GIS input/output interface is presented along with model validation on three basins within the Upper Trinity basin in Texas.     

MODELING THE EFFECT OF BRUSH CONTROL ON RANGELAND WATER YIELD1

ABSTRACT: With the increase in water demand in Texas, attention has turned to improving water yield by brush control on rangeland watersheds. Several hydrologic models have been developed for either farmland or rangeland. However, none of the models were specifically developed to assess the impact of brush control on rangeland water yield. Yet, modeling the impact of brush control on water yield needs to be considered if alternative techniques are to be compared. Two models, Ekalaka Rangeland Hydrology and Yield Model (ERHYM-II) and Simulator for Water Resources on Rural Basins (SWRRB) were selected. The Soil Conservation Service curve number (SCS-CN) method is used in both models to predict surface runoff from each rainfall event. The major differences between the ERHYM-II and SWRRB models are the evapotranspiration, soil water routing, and plant growth components. The models were evaluated on brush-dominated and chemically and mechanically brush-controlled range watersheds in Texas. Results indicated that both models were capable of simulating soil water and water yield from brush dominated and chemically brush-controlled range watersheds. The models were not able to predict water yield from the mechanically brush-controlled (root plowed) watershed with acceptable accuracy. The depressions that were caused by root plowing stored surface runoff and reduced water yield from the watershed. Information about the size of depressions was not available for further model evaluation.     

Life cycle assessment of the production and use of polypropylene tree shelters

A detailed Life Cycle Assessment (LCA) has been conducted for the manufacture, use and disposal of polypropylene tree shelters, which are used to protect young seedlings in the first few years of growth. The LCA was conducted using Simapro software, the Ecoinvent database and ReCiPe assessment methodology. Detailed information on materials, manufacturing, packaging and distribution of shelters was obtained from Tubex Ltd. in South Wales, UK. Various scenarios based on different forest establishment methods, with or without tree shelters were derived and analysed using data from published literature and independent sources. The scenarios included commercial forestry in northern temperate conditions, amenity forest establishment in temperate conditions, and forest establishment in semi-arid conditions. For commercial forestry, a reduction in required seedling production and planting as well as additional time-averaged wood production led to significant benefits with tree shelters, both compared to unprotected and fenced cases. For the amenity forest scenarios, tree shelter use had a net environmental impact, while for semi-arid forestry, the benefits of reduction in water use outweighed shelter production impacts. The current practice of in-situ degradation was compared to collection and disposal and it was found that in-situ degradation was slightly preferable in terms of overall environmental impact. Use of biopolymer-based shelters would improve the environmental performance slightly.     

Observed climate-induced changes in plant phenology in the Netherlands

We determined whether climate change in the Netherlands has caused phenological changes since 1868. We analysed over 150,000 plant phenological observations of 320 plant species, obtained by four volunteer networks and one series collected by Mr. Braaksma. With the network data, we compared the timing of life cycle events in three different periods: 1894–1932 (Period 1), 1940–1968 (Period 2) and 2001–2010 (Period 3). For the Braaksma series, we compared the periods 1953–1968 (Period A) with 1969–1992 (Period B). We conclude that until the beginning of the 1990s, there have been no significant changes in the timing of life cycle events. The timing of life cycle events in Period 3 showed an average advance of flowering, leaf unfolding and fruit ripening of 14 days compared with Period 1 and 13 days compared with Period 2. Some species have advanced up to over 35 days. Autumn events occurred up to an average of 7 days later in Period 3 compared to earlier periods. This study shows that, based on network data, changes in climate explain on average 66 % of the variation in timing of phenological events from year to year. For the Braaksma data, this is 38 %. The expected future changes in climate will undoubtedly result in a further lengthening of the growing season. We believe that phenological networks, supported by thousands of volunteers, are needed to quantify, analyse, predict and communicate these phenological changes so various sectors in society can adapt to these changes and prevent significant socio-economic impacts.     

Effects of roof and rainwater characteristics on copper concentrations in roof runoff

Copper sheeting is a common roofing material used in many parts of the world. However, copper dissolved from roof sheeting represents a source of copper ions to watersheds. Researchers have studied and recently developed a simple and efficient model to predict copper runoff rates. Important input parameters include precipitation amount, rain pH, and roof angle. We hypothesized that the length of a roof also positively correlates with copper concentration (thus, runoff rates) on the basis that runoff concentrations should positively correlate with contact time between acidic rain and the copper sheet. In this study, a novel system was designed to test and model the effects of roof length (length of roof from crown to the drip edge) on runoff copper concentrations relative to rain pH and roof angle. The system consisted of a flat-bottom copper trough mounted on an apparatus that allowed run length and slope to be varied. Water of known chemistry was trickled down the trough at a constant rate and sampled at the bottom. Consistent with other studies, as pH of the synthetic rainwater decreased, runoff copper concentrations increased. At all pH values tested, these results indicated that run length was more important in explaining variability in copper concentrations than was the roof slope. The regression equation with log-transformed data (R ² = 0.873) accounted for slightly more variability than the equation with untransformed data (R ² = 0.834). In log-transformed data, roof angle was not significant in predicting copper concentrations.     

Removal and formation of chlorinated triclosan derivatives in wastewater treatment plants using chlorine and UV disinfection

Triclosan, a common antimicrobial agent, may react during the disinfection of wastewater with free chlorine to form three chlorinated triclosan derivatives (CTDs). This is of concern because the CTDs may be photochemically transformed to tri- and tetra-chlorinated dibenzo-p-dioxins when discharged into natural waters. In this study, wastewater influent, secondary (pre-disinfection) effluent, and final (post-disinfection) effluent samples were collected on two occasions each from two activated sludge wastewater treatment plants, one using chlorine disinfection and one using UV disinfection. Concentrations of triclosan and three CTDs were determined using ultra performance liquid chromatography-triple quadrupole mass spectrometry with isotope dilution methodology. Triclosan and the CTDs were detected in every influent sample at levels ranging from 453 to 4530 and 2 to 98 ng L⁻¹, respectively, though both were efficiently removed from the liquid phase during activated sludge treatment. Triclosan concentrations in the pre-disinfection effluent ranged from 36 to 212 ng L⁻¹, while CTD concentrations were below the limit of quantification (1 ng L⁻¹) for most samples. In the treatment plant that used chlorine disinfection, triclosan concentrations decreased while CTDs were formed during chlorination, as evidenced by CTD levels as high as 22 ng L⁻¹ in the final effluent. No CTDs were detected in the final effluent of the treatment plant that used UV disinfection. The total CTD concentration in the final effluent of the chlorinating treatment plant reached nearly one third of the triclosan concentration, demonstrating that the chlorine disinfection step played a substantial role in the fate of triclosan in this system.