Escherichia coli loading at or near base flow in a mixed-use watershed

This study analyzed the occurrence of Escherichia coli in a mixed land-use watershed with human, cattle, and wildlife fecal inputs located in a karstic geologic region using synoptic monitoring (samples taken throughout the watershed system) during base-flow conditions. The objective of the study was to evaluate the occurrence of E. coli during base-flow conditions for several months at seven different main channel and nine different tributary sampling sites in the Stock Creek watershed, a 49.3-km(2) basin located in Knoxville, TN. Escherichia coli densities were measured using the Colilert (Defined Substrate Technology) method. The instantaneous loads for E. coli were determined from measured flow rates and E. coli densities, with the highest loading rates observed in the late fall. The study indicated a strong correlation between E. coli load rate (colony-forming units [CFU]/d), 7-d antecedent precipitation, and turbidity. Water quality data, however, also exhibited a spatial dependency; for example, the E. coli load rate was better correlated with turbidity in the slower draining basin tailwater sampling sites than in the faster draining upstream headwater sampling sites. In the headwater sites, the E. coli load rate was better correlated with 7-d antecedent precipitation than turbidity.     

Baseflow nitrate in relation to stream order and agricultural land use

Management of agricultural nonpoint-source pollution continues to be a challenge because of spatial and temporal variability. Using stream order as an index, we explored the distribution of nitrate concentration and load along the stream network of a large agricultural watershed in Pennsylvania-the East Mahantango Creek Watershed and two of its sub-watersheds. To understand nitrate concentration variation in the stream water contributed from ground water, this study focused on baseflow. Impacts of agricultural land use area on baseflow nitrate in the stream network were investigated. Nitrate concentration showed a general decreasing trend with increasing stream order based on stream order averaged values; however, considerable spatial and temporal variability existed within each snapshot sampling. Nitrate loads increased with stream order in a power function because of the dominant effect of stream flow rate over the nitrate concentration. Within delineated sub-watersheds based on stream orders, positive linear functions were found between agricultural land use area percentage and the baseflow nitrate concentration and between agricultural drainage area and the nitrate load. The slope of the positive linear regression between the baseflow nitrate concentration and percent agricultural land area seems to be a valuable indicator of a watershed's water quality as influenced by agricultural practices, watershed size, and specific physiographic setting. Stream order seems to integrate, to a certain degree, the source and transport aspects of nonpoint-source pollution on a yearly averaged basis and thus might provide a quick estimate of the overall trend in baseflow nitrate concentration and load distribution along complex stream networks in agricultural watersheds.     

Spatial and temporal drivers of zoonotic pathogen contamination of an agricultural watershed

In regions where animal agriculture is prominent, such as southern Alberta, higher rates of gastrointestinal illness have been reported when compared with nonagricultural regions. This difference in the rate of illness is thought to be a result of increased zoonotic pathogen exposure through environmental sources such as water. In this study, temporal and spatial factors associated with bacterial pathogen contamination of the Oldman River, which transverses this region, were analyzed using classification and regression tree analysis. Significantly higher levels of fecal indicators; more frequent isolations of Campylobacter spp., Escherichia coli O157:H7, and Salmonella enterica spp.; and higher rates of detection of pig-specific Bacteroides markers occurred at downstream sites than at upstream sites, suggesting additive stream inputs. Fecal indicator densities were also significantly higher when any one of these three bacterial pathogens was present and where there were higher total animal manure units; however, occasionally pathogens were present when fecal indicator levels were low or undetectable. Overall, Salmonella spp., Campylobacter spp., and E. coli O157:H7 presence was associated with season, animal manure units, and total rainfall on the day of sampling and 3 d in advance of sampling. Several of the environmental variables analyzed in this study appear to influence pathogen prevalence and therefore may be useful in predicting water quality and safety and in the improvement of watershed management practices in this and other agricultural regions.     

Chemical transport from paired agricultural and restored prairie watersheds

A five-year record of streamflow and chemical sampling data was evaluated to assess the effects of large-scale prairie restoration on transport of NO3-N, Cl, and SO4 loads from paired 5,000-ha watersheds located in Jasper County, Iowa. Water quality conditions monitored during land use conversion from row crop agriculture to native prairie in the Walnut Creek watershed were compared with a highly agricultural control watershed (Squaw Creek). Combining hydrograph separation with a load estimation program, baseflow and stormflow loads of NO3-N, Cl, and SO4 were estimated at upstream and downstream sites on Walnut Creek and a downstream site on Squaw Creek. Chemical export in both watersheds was found to occur primarily with baseflow, with baseflow transport greatest during the late summer and fall. Lower Walnut Creek watershed, which contained the restored prairie areas, exported less NO3-N and Cl compared with upper Walnut Creek and Squaw Creek watersheds. Average flow-weighted concentrations of NO3-N exceeded 10 mg/L in upper Walnut Creek and Squaw Creek, but were estimated to be 6.6 mg/L in lower Walnut Creek. Study results demonstrate the utility of partitioning loads into baseflow and stormflow components to identify sources of pollutant loading to streams.     

Stream Discharge and Riparian Land Use Influence In-Stream Concentrations and Loads of Phosphorus from Central Plains Watersheds

Total annual nutrient loads are a function of both watershed characteristics and the magnitude of nutrient mobilizing events. We investigated linkages among land cover, discharge and total phosphorus (TP) concentrations, and loads in 25 Kansas streams. Stream monitoring locations were selected from the Kansas Department of Health and Environment stream chemistry long-term monitoring network sites at or near U.S. Geological Survey stream gauges. We linked each sample with concurrent discharge data to improve our ability to estimate TP concentrations and loads across the full range of possible flow conditions. Median TP concentration was strongly linked (R ² = 76%) to the presence of cropland in the riparian zones of the mostly perennial streams. At baseflow, discharge data did not improve prediction of TP, but at high flows discharge was strongly linked to concentration (a threshold response occurred). Our data suggest that on average 88% of the total load occurred during the 10% of the time with the greatest discharge. Modeled reductions in peak discharges, representing increased hydrologic retention, predicted greater decreases in total annual loads than reductions of ambient concentrations because high discharge and elevated phosphorus concentrations had multiplicative effects. No measure of land use provided significant predictive power for concentrations when discharge was elevated or for concentration rise rates under increasing discharge. These results suggest that reductions of baseflow concentrations of TP in streams without wastewater dischargers may be managed by reductions of cropland uses in the riparian corridor. Additional measures may be needed to manage TP annual loads, due to the large percentage of the TP load occurring during a few high-flow events each year.     

Wildlife identified as major source of Escherichia coli in agriculturally dominated watersheds by BOX A1R-derived genetic fingerprints

The presence of Escherichia coli in recreational and potable waters is a major concern to the general public as elevated levels of E. coli suggest the presence of pathogenic bacteria and viruses. Unfortunately, traditional microbial techniques do not allow specific identification of the source of E. coli. This reduces the ability to target management practices that reduce bacterial contamination. In the Finger Lakes region of western New York, USA, wildlife resides in relatively high densities on watersheds dominated by people and dairy farms, and as a result, the sources of fecal degradation of potable and recreational waters are often unknown. In the Conesus Lake watershed, the sources of microbial contamination were assessed using Rep-PCR molecular tools, a method of amplifying repetitive DNA sequences found throughout the E. coli genome to produce distinct fingerprints for a given ecotype. Molecular fingerprints of E. coli isolated from regional populations of cattle, humans, geese and deer were compared to E. coli isolated from stream water samples. Canonical discriminant function analysis indicated that the DNA fingerprints of the original source group isolates were correctly predicted 90.2% of the time. Since land use in the sub-watersheds was dominated by dairy and cash crop farms, it was expected that the majority of E. coli isolated would be identified as cows; however, an unexpectedly high percentage of isolates were identified as wildlife (geese and deer). Geese were the dominant source of E. coli (44.7-73.7% of the total sources) in four sub-watersheds followed by cows (10.5-21.1%), deer (10.5-18.4%), humans (5.3-12.9%) and unidentifiable sources (0.0-11.8%). Management practices intended to decrease the number of cattle or the amount of manure spread in a sub-watershed were reflected in a decrease of E. coli ecotypes associated with dairy cows.     

Nitrogen loads through baseflow, stormflow, and underflow to Rehoboth Bay, Delaware

A detailed study of water and nitrogen (N) discharge from a small, representative subwatershed of Rehoboth Bay, Delaware, was conducted to determine total N loads to the bay. The concentrations of ammonium (NH4(+)), nitrate + nitrite (NO3(-) + NO2(-)), and dissolved and particulate organic N were determined in baseflow and storm waters discharging from Bundicks Branch from October 1998 to April 2002. A novel hydrographic separation model that accounts for significant decreases in baseflow during storm events was developed to estimate N loads during unsampled storms. Nitrogen loads based on gauged flows alone (7100-19,100 kg/yr) significantly underestimated those based on land use-land cover (LULC) and estimated N export factors from different classes of LULC (32,000-40,600 kg/yr). However, when ungauged underflow and associated N loads were included in the total loads (25,500-33,800 kg/yr), there was much better agreement with LULC export models. This suggests that in permeable coastal plain sediments, underflow contributes significantly to N fluxes to estuarine receiving waters, particularly in drier years. Based on the similarity in LULC, N loads from the Bundicks Branch subwatershed were used to estimate upland loads to the entire Rehoboth Bay Watershed (259,000-316,000 kg/yr). These N loads from the watershed were much greater than those from direct atmospheric deposition (49,000-64,500 kg/yr) and from a local wastewater treatment plant (9700-13,700 kg/yr). While the watershed was the principal source of N at all times during the year, the relative contributions from the watershed, wastewater, and direct atmospheric deposition varied predictably with season.     

Agricultural drainage ditches mitigate phosphorus loads as a function of hydrological variability

Phosphorus (P) loading from nonpoint sources, such as agricultural landscapes, contributes to downstream aquatic ecosystem degradation. Specifically, within the Mississippi watershed, enriched runoff contributions have far-reaching consequences for coastal water eutrophication and Gulf of Mexico hypoxia. Through storm events, the P mitigation capacity of agricultural drainage ditches under no-till cotton was determined for natural and variable rainfall conditions in north Mississippi. Over 2 yr, two experimental ditches were sampled monthly for total inorganic P concentrations in baseflow and on an event-driven basis for stormflows. Phosphorus concentrations, Manning's equations with a range of roughness coefficients for changes in vegetative densities within the ditches, and discharge volumes from Natural Resources Conservation Service dimensionless hydrographs combined to determine ranges in maximum and outflow storm P loads from the farms. Baseflow regressions and percentage reductions with P concentrations illustrated that the ditches alternated between being a sink and source for dissolved inorganic P and particulate P concentrations throughout the year. Storm event loads resulted in 5.5% of the annual applied fertilizer to be transported into the drainage ditches. The ditches annually reduced 43.92 +/- 3.12% of the maximum inorganic effluent P load before receiving waters. Agricultural drainage ditches exhibited a fair potential for P mitigation and thus warrant future work on controlled drainage to improve mitigation capacity.     

ENHANCING FECAL COLIFORM TOTAL MAXIMUM DAILY LOAD MODELS THROUGH BACTERIAL SOURCE TRACKING1

ABSTRACT: Surface water impairment by fecal coliform bacteria is a water quality issue of national scope and importance. In Virginia, more than 400 stream and river segments are on the Commonwealth's 2002 303(d) list because of fecal coliform impairment. Total maximum daily loads (TMDLs) will be developed for most of these listed streams and rivers. Information regarding the major fecal coliform sources that impair surface water quality would enhance the development of effective watershed models and improve TMDLs. Bacterial source tracking (BST) is a recently developed technology for identifying the sources of fecal coliform bacteria and it may be helpful in generating improved TMDLs. Bacterial source tracking was performed, watershed models were developed, and TMDLs were prepared for three streams (Accotink Creek, Christians Creek, and Blacks Run) on Virginia's 303(d) list of impaired waters. Quality assurance of the BST work suggests that these data adequately describe the bacteria sources that are impairing these streams. Initial comparison of simulated bacterial sources with the observed BST data indicated that the fecal coliform sources were represented inaccurately in the initial model simulation. Revised model simulations (based on BST data) appeared to provide a better representation of the sources of fecal coliform bacteria in these three streams. The coupled approach of incorporating BST data into the fecal coliform transport model appears to reduce model uncertainty and should result in an improved TMDL.     

Does Wetland Location Matter When Managing Wetlands for Watershed‐Scale Flood and Drought Resilience?

Wetland protection and restoration strategies that are designed to promote hydrologic resilience do not incorporate the location of wetlands relative to the main stream network. This is primarily attributed to the lack of knowledge on the effects of wetland location on wetland hydrologic function (e.g., flood and drought mitigation). Here, we combined a watershed‐scale, surface–subsurface, fully distributed, physically based hydrologic model with historical, existing, and lost (drained) wetland maps in the Nose Creek watershed in the Prairie Pothole Region of North America to (1) estimate the hydrologic functions of lost wetlands and (2) estimate the hydrologic functions of wetlands located at different distances from the main stream network. Modeling results showed wetland loss altered streamflow, decreasing baseflow and increasing stream peakflow during the period of the precipitation events that led to major flooding in the watershed and downstream cities. In addition, we found that wetlands closer to the main stream network played a disproportionately important role in attenuating peakflow, while wetland location was not important for regulating baseflow. The findings of this study provide information for watershed managers that can help to prioritize wetland restoration efforts for flood or drought risk mitigation.     

Agricultural practices influence flow regimes of headwater streams in western Iowa

Agricultural tillage influences runoff and infiltration, but consequent effects on watershed hydrology are poorly documented. This study evaluated 25 yr (1971-1995) hydrologic records from four first-order watersheds in Iowa's loess hills. Two watersheds were under conventional tillage and two were under conservation (ridge) tillage, one of which was terraced. All four watersheds grew corn (Zea mays L.) every year. Flow-frequency statistics and autoregressive modeling were used to determine how conservation treatments influenced stream hydrology. The autoregressive modeling characterized variations in discharge, baseflow, and runoff at multi-year, annual, and shorter time scales. The ridge-tilled watershed (nonterraced) had 47% less runoff and 36% more baseflow than the conventional watershed of similar landform and slope. Recovery of baseflow after drought was quicker in the conservation watersheds, as evidenced by 365-d moving average plots, and 67% greater baseflow during the driest 2 yr. The two conventional watersheds were similar, except the steeper watershed discharged more runoff and baseflow during short (<30 d), wet periods. Significant multi-year and annual cycles occurred in all variables. Under ridge-till, seasonal (annual-cycle) variations in baseflow had greater amplitude, showing the seasonality of subsurface contaminant movement could increase under conservation practices. However, deviations from the modeled cycles of baseflow were also more persistent under conservation practices, indicating baseflow was more stable. Indeed, flow-frequency curves showed wet-weather discharge decreased and dry-weather discharge increased under conservation practices. Although mean discharge increased in the conservation watersheds, variance and skewness of daily values were smaller. Ridge tillage with or without terraces increased stream discharge but reduced its variability.     

EFFECTS OF URBAN LAKES ON QUANTITY AND QUALITY OF BASEFLOW1

ABSTRACT: Man-made lakes have significant impacts on the hydrologic conditions in the watershed in which they are built. This paper examines the nature of the impact upon baseflow by comparing baseflow conditions at the outlet of the lakes with those elsewhere in the watershed. Situated in the upper reaches of a small watershed, the lakes studied have only a minor effect upon the magnitude of baseflow discharge, increasing it slightly from October to January, and decreasing it from May to September. Baseflow quality is substantially affected. Natural dissolved ions, as represented by magnesium, are generally decreased in concentration and total load by the lakes. Road salt related inons are substantially increased in both concentration and total load in the baseflow. Surface runoff stored in the lakes is extremely enriched in salt in the winter, and the storage capacity of the lakes is sufficient to maintain winter salt concentrations in the baseflow near the lakes until summer. The storage effect also tends to damp out seasonal fluctuations in baseflow chloride content which are extreme in suburban watersheds. The difference in quality between the lake and non-lake baseflows and the linear distance needed for complete mixing are used as measures of the magnitude and distal extent of the lake effect on baseflow quality.     

STREAMFLOW DEPLETION: MODELING OF REDUCED BASEFLOW ANI INDUCED STREAM INFILTRATION FROM SEASONALLY PUMPED WELLS1

ABSTRACT: Numerical modeling techniques are used to analyze streamflow depletion for stream‐aquifer systems with baseflow. The analyses calculated two flow components generated by a pumping well located at a given distance from a river that is hydraulically connected to an unconfined aquifer. The two components are induced stream infiltration and reduced baseflow; both contribute to total streamflow depletion. Simulation results suggest that the induced infiltration, the volume of water discharged from the stream to the aquifer, has a shorter term impact on streamflow, while the reduced baseflow curves show a longer term effect. The peak impacts of the two hydrologic processes on streamflow occur separately. The separate analysis helps in understanding the hydrologic interactions between stream and aquifer. Practically, it provides useful information about contaminant transport from stream to aquifer when water quality is a concern, and for areas where water quantity is an issue, the separate analysis offers additional information to the development of water resource management plan.     

ALAWAT: A spatially allocated watershed model for approximating stream,sediment, and pollutant flows in Hawaii,USA

The Ala Wai Canal Watershed Model (ALAWAT) is a planning-level watershed model for approximating direct runoff, streamflow, sediment loads, and loads for up to five pollutants. ALAWAT uses raster GIS data layers including land use, SCS soil hydrologic groups, annual rainfall, and subwatershed delineations as direct model parameter inputs and can use daily total rainfall from up to ten rain gauges and streamflow from up to ten stream gauges. ALAWAT uses a daily time step and can simulate flows for up to ten-year periods and for up to 50 subwatersheds. Pollutant loads are approximated using a user-defined combination of rating curve relationships, mean event concentrations, and loading/washoff parameters for specific subwatersheds, land uses, and times of year. Using ALAWAT, annual average streamflow and baseflow relationships and urban suspended sediment loads were approximated for the Ala Wai Canal watershed (about 10,400 acres) on the island of Oahu, Hawaii. Annual average urban suspended sediments were approximated using two methods: mean event concentrations and pollutant loading and washoff. Parameters for the pollutant loading and washoff method were then modified to simulate the effect of various street sweeping intervals on sediment loads.     

Evaluation of a denitrification wall to reduce surface water nitrogen loads

Denitrification walls have significantly reduced nitrogen concentrations in groundwater for at least 15 yr. This has spurred interest in developing methods to efficiently increase capture volume to reduce N loads in larger watersheds. The objective of this study was to maximize treatment volume by locating a wall where a large groundwatershed was funneled toward seepage slope headwaters. Nitrogen concentration and load were measured before and after wall installation in paired treatment and control streams. Beginning 2 d after installation, nitrogen concentration in the treatment stream declined from 6.7 ± 1.2 to 3.9 ± 0.78 mg L and total N loading rate declined by 65% (391 kg yr) with no corresponding decline in the control watershed. This wall, which only comprised 10 to 11% of the edge of field area that contributed to the treatment watershed, treated approximately 60% of the stream discharge, which confirmed the targeted approach. The total load reduction measured in the stream 155 m downstream from the wall (340 kg yr) was higher than that found in another study that measured load reductions in groundwater wells immediately around the wall (228 kg yr). This indicated the possibility of an extended impact on denitrification from carbon exported beyond the wall. This extended impact was inauspiciously confirmed when oxygen levels at the stream headwaters temporarily declined for 50 d. This research indicates that targeting walls adjacent to streams can effectively reduce N loading in receiving waters, although with a potentially short-term impact on water quality.     

Significant Escherichia coli attenuation by vegetative buffers on annual grasslands

A study was conducted to estimate the retention efficiency of vegetative buffers for Escherichia coli deposited on grasslands in cattle fecal deposits and subject to natural rainfall-runoff conditions. The study was conducted on annual grasslands in California's northern Sierra Nevada foothills, a region with a distinct wet-dry season Mediterranean climate. We used 48, 2.0- by 3.0-m runoff plots to examine the efficacy of 0.1-, 1.1-, and 2.1-m buffers at three land slopes (5, 20, and 35%) and four dry vegetation matter levels (225, 560, 900, and 4500 kg/ha) across 27 rainfall-runoff events during two rainfall seasons. Buffer width treatments were implemented by placement of cattle fecal material containing known loads of E. coli 0.1, 1.1, or 2.1 m upslope of the plot runoff collector. Mean total runoff to total rainfall ratio per plot ranged from 0.014:1 to 0.019:1 and reflected the high infiltration capacity of these soils. Approximately 94.8 to 99.995% of total E. coli load applied to each plot appears to be either retained in the fecal pat and/or attenuated within 0.1 m downslope of the fecal pat, irrespective of the presence of a wider vegetated buffer. Relative to a 0.1-m buffer, we found 0.3 to 3.1 log10 reduction in E. coli discharge per additional meter of vegetative buffer across the range of residual dry vegetation matter levels, land slope, and rainfall and runoff conditions experienced during this project. Buffer efficiency was significantly reduced as runoff increased. These results support the assertion that grassland buffers are an effective method for reducing animal agricultural inputs of waterborne E. coli into surface waters.     

Spatial and temporal modeling of microbial contaminants on grazing farmlands

This paper introduces an integrated spatial and temporal modeling system developed mathematically for assessing microbial contaminants on animal-grazed farmlands. The model uses fecal coliform, specifically Escherichia coli, as an indicator of fecal contamination and describes the sources, sinks, transport processes, and fate of E. coli contaminants in catchments and associated streams. Spatial features include grazing location, land topography, distance to a nearby stream, and distance through the stream network to the outlet. Temporal features are population dynamics on the land surface, in flow, and on streambeds. The model applies the principles of conservation of mass balance on two different types of pools: grid cells on land surfaces and networked stream segments. The model aims to improve the prediction of the effects of different land management strategies on the fecal contamination of waterways. This is achieved by characterizing the movement of fecal contaminants from land to streams and in-stream mobilization. Processes of attenuation, diffusion, and transport govern the movement. Our study site is a hill land catchment with an area of 140 ha and is used exclusively for animal grazing. The model was calibrated with previous research results, and then tested using the data collected at the outlet of the catchment. The sensitivity of the model predictions was analyzed for different scenarios: effect of stock rate, attenuation rate, and flow volumes. The similar pattern between monitored and predicted E. coli concentration proved that the model captures the key features that control the population dynamics of fecal contaminants. Further experiments are required to expand the model's functionality for covering more mitigation options.     

STREAM BASEFLOW PREDICTION BY CONVOLUTION OF ANTECEDENT RAINFALL EFFECTS1

ABSTRACT A method of stream baseflow prediction using a parallel drain theory and convolution techniques was developed. The infiltrating portions of several rain events were superimposed on the ground-water reserves and allowed to drain to the stream as individual baseflow responses. The convolution technique was used in summing the contributions from each rain event to the stream to give the total baseflow at any point in time. A single lumped parameter was adapted from a parallel drain analogy to represent the physical characteristics of a watershed. This parameter determines the time delay between a rainfall event and the resulting baseflow response. The procedure was applied to data from five watersheds. One year of records was used to find the best-fitting runoff delay coefficient, thus calibrating the response function which was subsequently applied to two test years to predict a dry weather low flow sequence. The agreement between predicted and observed flows was reasonably good, but marred by frequent minor rainfalls during the chosen dry periods. The application of the method should be much more successful in the western states where prolonged dry periods are common.     

Influences on Wood Load in Mountain Streams of the Bighorn National Forest,Wyoming, USA

We documented valley and channel characteristics and wood loads in 19 reaches of forested headwater mountain streams in the Bighorn National Forest of northern Wyoming. Ten of these reaches were in the Upper Tongue River watershed, which has a history of management including timber harvest, tie floating, and road construction. Nine reaches were in the North Rock Creek watershed, which has little history of management activities. We used these data to test hypotheses that (i) valley geometry correlates with wood load, (ii) stream gradient correlates with wood load, and (iii) wood loads are significantly lower in managed watersheds than in otherwise similar unmanaged watersheds. Statistical analyses of the data support the first and third hypotheses. Stream reaches with steeper valley side slopes tend to have higher wood loads, and reaches in managed watersheds tend to have lower wood loads than reaches in unmanaged watersheds. Results do not support the second hypothesis. Shear stress correlated more strongly with wood load than did stream gradient, but statistical models with valley-scale variables had greater explanatory power than statistical models with channel-scale variables. Wood loads in stream reaches within managed watersheds in the Bighorn National Forest tend to be two to three times lower than wood loads in unmanaged watersheds.     

Phosphorus export from an agricultural watershed: linking source and transport mechanisms

Many source and transport factors control P loss from agricultural landscapes; however, little information is available on how these factors are linked at a watershed scale. Thus, we investigated mechanisms controlling P release from soil and stream sediments in relation to storm and baseflow P concentrations at four flumes and in the channel of an agricultural watershed. Baseflow dissolved reactive phosphorus (DRP) concentrations were greater at the watershed outflow (Flume 1; 0.042 mg L(-1)) than uppermost flume (Flume 4; 0.028 mg L(-1)). Conversely, DRP concentrations were greater at Flume 4 (0.304 mg L(-1)) than Flume 1 (0.128 mg L(-1)) during stormflow. Similar trends in total phosphorus (TP) concentration were also observed. During stormflow, stream P concentrations are controlled by overland flow-generated erosion from areas of the watershed coincident with high soil P. In-channel decreases in P concentration during stormflow were attributed to sediment deposition, resorption of P, and dilution. The increase in baseflow P concentrations downstream was controlled by channel sediments. Phosphorus sorption maximum of Flume 4 sediment (532 mg kg(-1)) was greater than at the outlet Flume 1 (227 mg kg(-1)). Indeed, the decrease in P desorption between Flumes 1 and 4 sediment (0.046 to 0.025 mg L(-1)) was similar to the difference in baseflow DRP between Flumes 1 and 4 (0.042 to 0.028 mg L(-1)). This study shows that erosion, soil P concentration, and channel sediment P sorption properties influence streamflow DRP and TP. A better understanding of the spatial and temporal distribution of these processes and their connectivity over the landscape will aid targeting remedial practices.