SPARROW Modeling of Nitrogen Sources and Transport in Rivers and Streams of California and Adjacent States, U.S.

Abstract

The SPARROW (SPAtially Referenced Regressions On Watershed attributes) model was used to evaluate the spatial distribution of total nitrogen (TN) sources, loads, watershed yields, and factors affecting transport and decay in the stream network of California and portions of adjacent states for the year 2002. The two major TN sources to local catchments on a mass basis were fertilizers and manure (51.7%) and wastewater discharge (15.9%). Other sources contributed < 12%. Fertilizer use is widespread in the Central Valley region of California, and also important in several other regions because of the diversity of California agriculture. Precipitation, sand content of surficial soils, wetlands, and tile drains were important for TN movement to stream reaches. Median streamflow in the study area is about 0.04 m3/s. Aquatic losses of nitrogen were found to be most important in intermittent and small to medium sized streams (0.2‐14 m3/s), while larger streams showed less loss, and therefore are important for TN transport. Nitrogen loss in reservoirs was found to be insignificant, possibly because most of the larger ones are located upstream of nitrogen sources. The model was used to show loadings, sources, and tributary inputs to several major rivers. The information provided by the SPARROW model is useful for determining both the major sources contributing nitrogen to streams and the specific tributaries that transport the load.

Nutrient Dynamics of the Delta: Effects on Primary Producers

“…The SPARROW model results also showed evidence of nitrogen retention within the aquatic system in small and medium-sized streams (Mulholland et al 2008), but little retention in rivers. Retention for both P and N in reservoirs was also found to be small, largely because the reservoirs are located above most cultivated lands Saleh and Domagalski 2015).…”

“…Publicly Owned Treatment Works (POTWs) are estimated to supply approximately 25% of the total nitrogen (TN) and 20% of the total phosphorus (TP) loads to the Delta, combining all upstream and in-Delta sources Saleh and Domagalski 2015). The Sacramento Regional Wastewater Treatment Plant (SRWTP) contributes about 90% of the annual total ammonia load to the Delta with effluent discharge occurring in the Sacramento River at Freeport in the north Delta (Jassby 2008).…”

“…Average values declined in the winter months, particularly at low flows. Saleh and Domagalski (2015) studied nitrogen sources and transport in the rivers and streams of California, including the major inputs to the Delta, using the SPAtially Referenced Regressions On Watershed (SPARROW) attributes modeling framework. They found that agricultural lands comprised the largest source (47%) of TN to the Delta in the Sacramento River drainage, with point sources (chiefly POTWs) accounting for 32%.…”

An introduction to high-frequency nutrient and biogeochemical monitoring for the Sacramento–San Joaquin Delta, northern California

“…Many factors interact to shape the Delta environment, including tides, river inflows, exports, salinity gradients, nutrients, suspended sediments, temperature, contaminants, invasive species, harmful algal blooms, channel geometry, island drainage, and other factors affecting physical and biological processes. In terms of annual loads, Central Valley watersheds are the largest contributor of nutrients to the Delta Saleh and Domagalski, 2015;Schlegel and Domagalski, 2015). Urban inputs from publicly owned treatment works (POTWs, commonly referred to as WWTPs) also are a major source of nutrients.…”

Designing a high-frequency nutrient and biogeochemical monitoring network for the Sacramento–San Joaquin Delta, northern California

“…In contrast, they are included in Sacramento River loads calculated downstream of the WWTP discharge location at approximately river mile 44 (Station C3; Novick and others, 2015;Saleh and Domagalski, 2015). When deciding on the specific location of monitoring stations that will represent nutrient inputs to the Delta, it is important for managers to agree on whether they want to focus on a site representing the most upstream point of the legally defined Delta or a point farther downstream that might better meet the monitoring objectives.…”