Water quality assessment of the San Joaquin-Tulare basins, California: Analysis of available data on nutrients and suspended sediment in surface water, 1972-1990

2005

SFEWS

As in many U.S. estuaries, the tidal San Joaquin River exhibits elevated organic matter production that interferes with beneficial uses of the river, including fish spawning and migration. High phytoplankton biomass in the tidal river is consequently a focus of management strategies. An unusually long and comprehensive monitoring dataset enabled identification of the determinants of phytoplankton biomass. Phytoplankton carrying capacity may be set by nitrogen or phosphorus during extreme drought years but, in most years, growth rate is light-limited. The size of the annual phytoplankton bloom depends primarily on river discharge during late spring and early summer, which determines the cumulative light exposure in transit downstream. The biomass-discharge relationship has shifted over the years, for reasons as yet unknown. Water diversions from the tidal San Joaquin River also affect residence time during passage downstream and may have resulted in more than a doubling of peak concentration in some years. Dam construction and accompanying changes in storageand-release patterns from upstream reservoirs have caused a long-term decrease in the frequency of large blooms since the early 1980s, but projected climate change favors a future increase. Only large decreases in nonpoint nutrient sources will limit phytoplankton biomass reliably. Growth rate and concentration could increase if nonpoint source management decreases mineral suspensoid load but does not decrease nutrient load sufficiently. Small changes in water storage and release patterns due to dam operation have a major influence on peak phytoplankton biomass, and offer a near-term approach for management of nuisance algal blooms.

Section: Discussion Nutrient Management and Phytoplanktonsupporting

confidence: 73%

Section: Discussion Nutrient Management and Phytoplanktonmentioning

confidence: 99%

Phytoplankton Regulation in a Eutrophic Tidal River (San Joaquin River, California)

2005

SFEWS

“…Lehman (2000) recently summarized long-term changes in phytoplankton community composition for the Delta, emphasizing the effects of climatic variability. Kratzer and Shelton (1998) describe nutrient sources and trends in San Joaquin River nutrient levels since the early 1950s. Fertilizer runoff, subsurface agricultural drainage, wastewater treatment plant discharges, and runoff from dairies have contributed to increasing concentrations over the last 50 yr.…”

mentioning

confidence: 99%

Annual primary production: Patterns and mechanisms of change in a nutrient‐rich tidal ecosystem

Limnology & Oceanography

Cloern

Cole

2002

205

194

Although nutrient supply often underlies long-term changes in aquatic primary production, other regulatory processes can be important. The Sacramento-San Joaquin River Delta, a complex of tidal waterways forming the landward portion of the San Francisco Estuary, has ample nutrient supplies, enabling us to examine alternate regulatory mechanisms over a 21-yr period. Delta-wide primary productivity was reconstructed from historical water quality data for 1975-1995. Annual primary production averaged 70 g C m Ϫ2 , but it varied by over a factor of five among years. At least four processes contributed to this variability: (1) invasion of the clam Potamocorbula amurensis led to a persistent decrease in phytoplankton biomass (chlorophyll a) after 1986; (2) a long-term decline in total suspended solids-probably at least partly because of upstream dam construction-increased water transparency and phytoplankton growth rate; (3) river inflow, reflecting climate variability, affected biomass through fluctuations in flushing and growth rates through fluctuations in total suspended solids; and (4) an additional pathway manifesting as a long-term decline in winter phytoplankton biomass has been identified, but its genesis is uncertain. Overall, the Delta lost 43% in annual primary production during the period. Given the evidence for food limitation of primary consumers, these findings provide a partial explanation for widespread Delta species declines over the past few decades. Turbid nutrient-rich systems such as the Delta may be inherently more variable than other tidal systems because certain compensatory processes are absent. Comparisons among systems, however, can be tenuous because conclusions about the magnitude and mechanisms of variability are dependent on length of data record.Phytoplankton primary productivity in lakes, estuaries, and the ocean plays an essential role in element cycling, water quality, and food supply to heterotrophs (Cloern 1996). Although we implicitly recognize primary productivity as a time-varying process, much of our effort to measure and understand this variability has focused on time scales of 1 yr or less. How much does annual primary production vary from year to year or over periods of decades, and what are the underlying mechanisms of variability at these longer time scales? These time scales are of particular interest from a practical viewpoint: they span the period over which we must separate anthropogenic influences from natural variability in order to understand the effects of our current use of water resources. Long-term studies of annual primary production in individual systems can also help us to understand

“…Ammonium accounts for 20% and presumably dissolved organic matter the remaining 20%. The latter two could be in part extracellular and degradation products of phytoplankton and phytodetritus, but probably originate directly from agricultural sources, including animal wastes (Kratzer and Shelton 1998;Kratzer and others 2004). Insofar as these other sources do not covary with phytoplankton, they are a source of uncertainty in the analyses and models of this study.…”

Section: Causal Factorsmentioning

confidence: 99%

“…Nitrogen from animal wastes leaking directly to surface waters or first volatilizing as ammonia is often the largest single source for estuaries. The San Joaquin River watershed is no different in this respect, with much if not most of the nitrogen originating as animal waste (Kratzer and Shelton 1998;Kratzer and others 2004). The complexity of controlling mechanisms, though, which it shares with other dredged river channels receiving agricultural and wastewater inputs, has stimulated a large amount of diverse monitoring, experimentation, and modeling.…”

Section: Management Scenariosmentioning

confidence: 99%

Low Dissolved Oxygen in an Estuarine Channel (San Joaquin River, California): Mechanisms and Models Based on Long-Term Time Series

Nieuwenhuyse²

2005

SFEWS

The Stockton Deep Water Ship Channel, a stretch of the tidal San Joaquin River, is frequently subject to low dissolved oxygen conditions and annually violates regional water quality objectives. Underlying mechanisms are examined here using the long-term water quality data, and the efficacy of possible solutions using time-series regression models. Hypoxia is most common during June-September, immediately downstream of where the river enters the Ship Channel. At the annual scale, ammonium loading from the Regional Wastewater Control Facility has the largest identifiable effect on year-toyear variability. The longer-term upward trend in ammonium loads, which have been increasing over 10% per year, also corresponds to a longer-term downward trend in dissolved oxygen during summer. At the monthly scale, river flow, loading of wastewater ammonium and river phytoplankton, Ship Channel temperature, and Ship Channel phytoplankton are all significant in determining hypoxia. Over the recent historical range , wastewater ammonium and river phytoplankton have played a similar role in the monthly variability of the dissolved oxygen deficit, but river discharge has the strongest effect. Model scenarios imply that control of either river phytoplankton or wastewater ammonium load alone would be insufficient to eliminate hypoxia. Both must be strongly reduced, or reduction of one must be combined with increases in net discharge to the Ship Channel. Model scenarios imply that preventing discharge down Old River with a barrier markedly reduces hypoxia in the Ship Channel. With the Old River barrier in place, unimpaired or full natural flow at Vernalis would have led to about the same frequency of hypoxia that has occurred with actual flows since the early 1980s.