Phytoplankton Fuels Delta Food Web

RESEARCH ARTICLE

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Phytoplankton fuels Delta food web

smelt (Hypomesus transpacificus), and commercial species such as chinook Alan D. Jassby salmon (Oncorhynchus tshawytscha) all James E. Cloern show evidence of food limitation dur- Anke B. Müller-Solger ing their first year. Zooplankton, a key ▼ food for young fishes, has also declined (Orsi and Mecum 1996). Some declining zooplankters, especially a mysid shrimp Populations of certain fishes and in- (Neomysis mercedis) and smaller species, also appear to be limited by food supply, vertebrates in the Sacramento-San as does the clam Corbicula fluminea, a Joaquin Delta have declined in abun- dominant benthic invertebrate. dance in recent decades and there is Zooplankton, benthic invertebrates William Sobzcak, former U.S. Geological evidence that food supply is partly Survey postdoctoral researcher, samples for and the larger, more visible fish and responsible. While many sources of zooplankton in the Delta. waterfowl that feed on them form a organic matter in the Delta could be food web that depends ultimately on in- supporting fish populations indi- he Sacramento–San Joaquin River puts of organic matter at its base (fig. 2). In many systems, phytoplankton spe- rectly through the food web (includ- TDelta is a complex mosaic of waterways that forms the transition zone be- cies play a fundamental role in the or- ing aquatic vegetation and decaying tween San Francisco Bay and its water- ganic matter supply to food webs. organic matter from agricultural shed (fig. 1). Over the last century, the These microscopic plants are respon- drainage), a careful accounting original dominant marsh habitat has sible for primary production, the pho- shows that phytoplankton is the been lost through filling and diking. tosynthetic production of organic dominant food source. Phytoplank- Water flows have changed radically. matter. Other sources of organic matter ton, communities of microscopic Exotic plants and animals have invaded are often present, however, and can free-floating algae, are the most im- or been introduced intentionally, and even be dominant, especially in estuar- toxic contaminants have become wide- ies. In fact, there has been speculation portant food source on a Delta-wide spread (CALFED 2000). The Delta is for many years that organic matter car- scale when both food quantity and now a focus of ecosystem restoration ried in from upstream and from adja- quality are taken into account. These because these changes have been ac- cent terrestrial sources is the main microscopic algae have declined companied by declines in the abun- source sustaining the Delta’s food web. since the late 1960s. Fertilizer and dance of many fish species that use What, then, are the relative roles played pesticide runoff do not appear to the Delta as a migration route, nursery by phytoplankton and other sources in be playing a direct role in long-term or permanent habitat. Some species the organic matter supply to Delta wa- phytoplankton changes; rather, (thicktail chub) have already become terways? The question is a basic one for extinct; others (winter-run chinook restoration of the Delta, because it de- species invasions, increasing water salmon) are now at risk of extinction; termines the focus for increasing food transparency and fluctuations in and still others (splittail, striped bass) supply to declining populations. In ad- water transport are responsible. have dramatically reduced popula- dition to investigating this, we examine Although the potential toxicity of tions. evidence for a long-term decline in the herbicides and pesticides to plank- Several lines of evidence suggest primary food supply and consider the ton in the Delta is well documented, that food limitation has played a role in role of agriculture. these declines. Many fish populations the ecological significance remains Food comes in many forms speculative. Nutrient inputs from ag- in the Delta are declining because of poor survival during the first year of To determine the most important or- ricultural runoff at current levels, in life, which can be caused by food short- ganic matter sources for Delta water- combination with increasing trans- ages (Bennett and Moyle 1996). Sport ways, we combined decades of data parency, could result in harmful al- fish such as striped bass (Morone collected by the California Department gal blooms. saxatilis), native species such as delta of Water Resources (CDWR), U.S. Bu-

104 CALIFORNIA AGRICULTURE, VOLUME 57, NUMBER 4 Glossary reau of Reclamation (USBR) and Algae: Primitive plants usually living in U.S. Geological Survey (USGS), water and occurring as single cells, using a variety of estimation tech- filaments, colonies and irregular aggregations. niques (Jassby and Cloern 2000). Aquatic vascular plant: Higher plants Organic matter sources are usually living in water bodies. May be free- compared in terms of their total organic floating or rooted. Also known as carbon (TOC) content; TOC can come aquatic macrophytes. in both particulate (POC) and dis- Benthic invertebrates: Invertebrates solved (DOC) forms. River input — living on or in the bottom sediments. organic material carried in by the Sac- Benthic microalgae: Microscopic algae ramento, San Joaquin and other rivers living on or just under the surface of the bottom sediments. and creeks — is the largest TOC source overall (fig. 3). Some of this river-borne Biomass: The weight of biological matter, usually measured in terms of material is actually phytoplankton and carbon, dry weight or fresh weight, and phytoplankton-derived detritus trans- expressed on an areal (g m-2) or ported from upstream of the Delta. -3 volumetric (mg m ) basis. Phytoplankton production within Chlorophyll: A green pigment present the Delta and organic matter in agricul- in most plants and essential for the process of photosynthesis, by which tural drainage directly into the Delta these plants obtain most if not all of are next in importance. Agricultural their energy. Chlorophyll a is one form drainage upstream of the Delta is in- that is often assumed an approximate cluded in river inputs and cannot be index of algal biomass. estimated separately with any confi- Detritus: Nonliving particulate and dence. Much of the organic matter in dissolved organic matter. agricultural drainage originates from Metazoa: Multicellular animals, in leaching of DOC from island peat soils. Fig. 1. The Sacramento-San Joaquin River Delta contrast to the more primitive extends upstream from Chipps Island to include protozoa. Discharge from wastewater treatment leveed islands, river channels, sloughs, flooded Phytoplankton: The plant plankton, plants, drainage from tidal marshes islands and tidal marshes. Boxes mark stations consisting mostly of microscopic algae. and production of aquatic vascular used by the California Department of Water Resources to assess water quality, in some Plankton: The community of passively plants such as the submerged Egeria cases since the late 1960s. suspended or only weakly swimming densa are tertiary sources. Urban run- organisms in a body of water, which off, primary production by benthic drift along with the water currents; microalgae and other sources — dominant among external sources (fig. 3). planktonic organisms range in size from tiny plants and animals to large although sometimes important in other Many of these sources are distributed jellyfish, and include the larval stages estuaries — are negligible sources of or- unevenly throughout the Delta, and we of many fishes. ganic matter in the Delta. Phytoplank- can identify areas where aquatic vascu- Primary productivity: The rate at ton is clearly the Delta’s dominant lar plants, tidal marsh drainage or an- which plants incorporate inorganic primary producer, whereas river input other source may dominate at times. carbon into organic matter. Usually measured on a volumetric (mg C m-3 d-1) of organic material from upstream is Nevertheless, phytoplankton produc- or areal (mg C m-2 yr-1) basis. Primary production is often used to refer separately to the amount of organic carbon produced in a particular time interval (mg C m-3 or mg C m-2). Protozoa: Single-celled animals, including amoeba, ciliates and flagellates in aquatic systems. Suspended sediments: Small mineral (clay and silt) particles suspended in waters. Turbidity: The scattering effect that suspended and dissolved solids have on light, imparting a cloudy appearance to water. Primary contributors include suspended sediments, soluble colored organic compounds and microscopic Fig. 2. The metazoan food web can be Fig. 3. Organic matter, measured as total organisms. extremely complex, especially in estuaries, organic carbon (TOC), is produced in Delta Zooplankton: The animal plankton, in and only a small portion of the Delta’s food waterways by photosynthesis and enters from estuaries consisting mostly of protozoa, web is portrayed here. The energy and a variety of external sources. Phytoplankton is rotifers and two crustacean types, the nutrient needs of the metazoan food web the biggest internal source and river transport cladocerans and the copepods. are supported by a variety of organic matter is the biggest external source. Error bars sources. represent standard error among years.

http://danr.ucop.edu/calag • OCTOBER-DECEMBER 2003 105 tion, river inputs and agricultural tastes and odors, and contributing dan- phytoplankton production is compa- drainage together account for 90% of gerous substances directly to raw water, rable to and sometimes greater than average annual Delta-wide organic such as the liver toxin microcystin-LR river inputs in spring and summer of matter sources. and neurotoxin anatoxin. On the posi- both above-normal and below-normal tive side, phytoplankton is central in years. Spring and summer are particu- Drinking water and organic matter the bioconcentration of contaminants, larly critical seasons for survival and Aside from its ecological signifi- transport and cycling of plant nutri- growth of young fish and successful re- cance, organic matter also has implica- ents, and the atmospheric carbon cruitment to fish populations. In contrast, tions for drinking-water quality in the dioxide balance. agricultural drainage is almost never a Delta. The Delta provides all or part significant source of bioavailable or- of the drinking-water supply for about An inefficient food source ganic matter. Consequently, plans to 22 million California residents. When The bulk accounting in figure 3 is an control organic matter in agricultural disinfectants such as chlorine are added inadequate guide to the relative value and Delta island drainage because of the to drinking water to kill microbial of different organic materials for pri- DBP problem should have little impact pathogens, they react with bromide and mary consumers such as zooplankton on food supply to the Delta’s food web. naturally occurring organic matter to and clams. Particulate and dissolved Recently this work was corroborated form disinfection byproducts (DBPs). forms of organic matter differ mark- with an extensive set of bioassays that The main DBP groups are total edly in their availability to the food assessed the food value of the Delta’s trihalomethanes, haloacetic acids, bro- web, making further refinement neces- organic matter sources (Sobczak et al. mate and chlorite. When these are con- sary. POC enters the Delta mostly as 2002). Although dissolved organic mat- sumed over years in excess of federal phytoplankton, bacteria and protozoa, ter is the major energy and carbon standards, some people may experience particles of decaying organic matter, source for bacterial metabolism, the problems with the liver, kidneys or cen- and suspended mineral particles carry- dominant food supply to the planktonic tral nervous system, or may have an in- ing organic matter on their surfaces. food web is bioavailable, particulate or- creased risk of cancer or anemia (Bull These particles can be utilized directly ganic matter derived primarily from in- and Kopfler 1991). by primary consumers such as clams ternal phytoplankton production. A current major challenge for water and zooplankton. suppliers in the Delta and elsewhere is In contrast, most dissolved organic Differing nutritional quality how to balance the risks from patho- carbon must first be transformed into Just as dissolved organic-matter gens and DBPs; it is important to pro- particles before it can be consumed. sources contribute little to the food vide protection from these pathogens This transformation happens primarily supply compared with particulate by using disinfectants while simulta- via the uptake and metabolism of DOC sources, the particulate sources them- neously containing health risks from by bacteria; in other words, the DOC is selves vary in quality. Delta phy- DBPs. One way to limit DBP formation converted to bacteria cells. Much of the toplankton are a better food source is to limit TOC levels in raw water sup- DOC is not very bioavailable (not easily for zooplankton than other kinds of plies. Our organic matter assessment assimilated and metabolized) and is particles in the POC pool — decaying implies that phytoplankton production, simply flushed downstream before bac- organic matter, bacteria and organic river-borne loading and agricultural teria can utilize it. Moreover, much of matter clinging to the surface of clay drainage should each be a focus of the remaining DOC that is metabolized and silt particles. The zooplankter source-control measures with respect to by bacteria is lost to respiration and Daphnia magna, which occurs in the the DBP problem: they are all impor- does not end up as bacterial biomass. Delta, feeds nonselectively on particles tant sources of naturally occurring or- We refined our estimates of the three smaller than 40 micrometers (µm). In a ganic matter in the Delta. major organic-matter sources by ac- series of laboratory feeding assays The participation of phytoplankton counting for bioavailability of DOC and (Müller-Solger et al. 2002), Daphnia in ecosystem food supply and drinking- respiratory losses, based on generaliza- were exposed using a flow-through water quality points to one example of tions from previous empirical studies system to water from four Delta habitat conflicting aims in the Delta. Although (Jassby and Cloern 2000). We then cat- types collected during all four seasons, higher phytoplankton production may egorized each year as either drier or and growth rates were measured. be a boon to certain food-limited organ- wetter than average and plotted the re- While POC concentrations were only isms, it can degrade drinking-water fined estimates of TOC in each category weakly related to Daphnia growth, con- quality through the formation of DBPs. by season (fig. 4). The relative impor- centrations up to a threshold of about The diversity of issues in the Delta cre- tance of organic matter sources changes 10 µg/L chlorophyll a — a pigment ates a complex balancing problem: hu- dramatically because so much of river found in phytoplankton — predicted man health versus ecosystem health. input and agricultural drainage is in Daphnia growth rates across all habitats The balancing of different aims is par- dissolved form. Phytoplankton produc- and seasons (fig. 5). Chlorophyll is not a ticularly difficult with regard to phy- tion is seen as a significant source of nutrient; it is merely a marker for the toplankton, which has many other bioavailable organic matter in all sea- phytoplankton fraction of particulate or- effects. Negative impacts include clog- sons, except for winters with above- ganic matter and a convenient way to es- ging filters, producing undesirable normal precipitation. Moreover, timate phytoplankton biomass. The

106 CALIFORNIA AGRICULTURE, VOLUME 57, NUMBER 4 )

1 0.5 −

0.4

0.3 Zooplankton growth rate (d 0.2

Fig. 4. Phytoplankton net primary productivity (NPP), river loading 515250 100 200 300 and agricultural drainage make up most of the bulk organic-matter Chlorophyll a (µg/L) Partic. organic carbon (mg/L) supply. The values shown here have been corrected for losses due to lack of bioavailability and respiration, and are therefore a more realistic comparison of the food value for consumer organisms than Fig. 5. The growth of the zooplankter Daphnia magna in Delta the bulk data of figure 3. Phytoplankton provides a significant waters is closely related to the supply of phytoplankton, as source especially in spring and summer, a critical period for indexed by chlorophyll a concentrations, but not so closely tied to populations of many fishes and invertebrates. levels of particulate organic carbon in general.

actual nutritional factors in phytoplank- tions in later years. In fact, all except losses due to consumption by clams, ton determining Daphnia growth rates spring months (April to June) showed a but apparently not by enough to are not known for certain, although ele- robust, statistically significant down- prevent a decrease in phytoplankton ments such as phosphorus and certain ward movement from 1975 to 1995 biomass. The dry weight of suspended essential fatty acids are candidates. (Jassby et al. 2002). Phytoplankton vari- mineral particles is much greater than ability could therefore easily lead to a phytoplankton biomass: variations in Supply changes year to year several-fold difference in zooplankton the latter have relatively little effect on Phytoplankton are probably the growth rates. transparency. most important portion of the particu- What are the reasons for this vari- late organic matter supply to the ability? In 1986, an Asian clam Impact of agricultural runoff Delta’s food web on a Delta-wide basis, (Potamocorbula amurensis) invaded and Dissolved organic matter in agricul- and growth rates of primary consumers established itself in Suisun Bay, pre- tural drainage, although an important such as Daphnia are closely tied to phy- sumably after being discharged with issue for drinking-water quality, is not toplankton availability below about ship ballast water. Its establishment a significant source of energy for the 10 µg/L. But how often is Delta phy- and dispersal were aided by the pro- Delta’s food web. What effects might toplankton at levels that can limit longed drought and accompanying low other constituents of drainage and runoff, zooplankton growth, and is phytoplank- freshwater inflows to the Delta that be- namely pesticides and nutrients, have on ton variable enough to induce major gan in 1987. Potamocorbula turned out to phytoplankton productivity? changes in zooplankton growth rates? In be a voracious consumer of phytoplank- Pesticide toxicity. Herbicide concen- fact, Delta chlorophyll levels quite com- ton and changed phytoplankton dynam- trations may limit phytoplankton monly fall within the range limiting ics in Suisun Bay (Alpine and Cloern growth rates during localized occur- growth. Thousands of chlorophyll a mea- 1992). The effects of Potamocorbula prob- rences of elevated concentrations. In surements have been made in the Delta ably extend into the western Delta, with 1997, Jody Edmunds and colleagues at since the late 1960s by the CDWR and a summer downturn after 1986 even in the USGS examined 53 water samples USBR, and 55% to 93% of them, depend- the Delta-wide chlorophyll record (fig. 6); collected from May through September ing on the year, are below 10 µg/L Potamocorbula are feeding most actively at nine Delta sites for six herbicides that (Jassby et al. 2002). Moreover, large during summer. inhibit photosynthesis. Only one swings have occurred in Delta-wide chlo- A recent analysis identified the most sample exceeded concentrations (diu- rophyll from one year to the next, and important driving forces for Delta-wide ron) reported to inhibit primary pro- longer-term changes are evident. phytoplankton production: interannual duction in laboratory experiments Figure 6 shows the annual average variability of water flow; increased con- (Edmunds et al. 1999). Similarly, bioas- of Delta-wide chlorophyll for each sea- sumption by Potamocorbula; and a says showed no relationship between son during a period when analytical downward trend in suspended mineral ambient herbicide concentrations and methods remained the same and sam- particles over many decades, which im- photosynthesis, except for this one pling was sufficiently comprehensive to proves water transparency and there- sample. The study design might have cover the entire Delta. Although the fore phytoplankton photosynthesis and missed herbicide runoff events during trend is not uniformly downward, growth rate (Jassby et al. 2002). The in- the rainy season. there has been an overall tendency to- crease in phytoplankton growth rate In fact, Jeff Miller and others from ward lower phytoplankton concentra- partially compensates for increased the Central Valley Regional Water

http://danr.ucop.edu/calag • OCTOBER-DECEMBER 2003 107 legacy of the erosion caused by hydraulic mining in the Sierra Nevada in the 19th century. By decreasing transparency and limiting the penetration of sunlight, turbidity slows phytoplankton photosynthesis and limits its ability to reproduce rapidly to massive levels. However, suspended sediment in the Delta has been decreasing and transparency increasing for decades. USGS scientists have identified several possible explanations for this phenomenon (Wright and Schoellhamer in press). First, reservoirs have been trap- ping sediment behind dams similar to the decrease in sediment load over the past 50 years. Second, there are still Fig. 6. Average chlorophyll a, and therefore phytoplankton biomass, is highly variable from season to season and year to year in the Delta, but in general it has been channel and floodplain deposits of decreasing since at least the 1970s. Summer chlorophyll, in particular, decreased mining-derived sediments that are markedly after the Asian clam, Potamocorbula amurensis, invaded in 1986; the clams being eroded and gradually depleted. feed most actively during summer. Third, bank stabilization such as rip- rap retards meandering, eliminating a sediment source (channel banks) and Quality Control Board, using an algal mation that pesticides in surface-water contributing to decreasing sediment indicator species, found toxicity in 22% runoff can be toxic to invertebrates in yield. Finally, the depositional nature of samples from the Sacramento–San the San Francisco Bay and Delta, the of the lower Sacramento floodplain has Joaquin watershed and Delta during ecological significance has not yet been changed in a way that, in principle, 2000 to 2001 (Miller et al. 2002). Again, established. could trap additional sediment. The diuron — an herbicide applied to Nutrient levels. Largely because of relative importance of these mecha- rights-of-way, alfalfa, vineyards and agricultural drainage, nutrient supplies nisms is not known precisely. In any orchards — was implicated. Most toxic- are well in excess of phytoplankton case, given the excess of nutrients in the ity occurred from January to March needs in the Delta. The availability of Delta, decreasing turbidity means that when diuron is applied and when it is nitrogen and phosphorus are important large phytoplankton blooms may be- most likely to rain in California; in con- determinants of phytoplankton growth come a more common phenomenon trast, most phytoplankton production and biomass in many aquatic systems. (Jassby et al. 2002). Moreover, Delta takes place in spring and summer. The A low nutrient supply can restrict the waters are warming, and higher tem- ecological consequences of this photosyn- growth of phytoplankton and, ulti- peratures favor the cyanobacteria (blue- thetic inhibition may therefore be limited. mately, fish yield. We found that nutri- green algae) that constitute nuisance or Pesticides may also affect primary ent concentrations were low enough to harmful algal blooms. If such nuisance production through indirect effects on limit phytoplankton growth for only or harmful blooms become common, the zooplankton community, molluscs about 0.1% of the measurements since control of nitrogen and phosphorus in- and other organisms that feed on phy- the late 1960s, most occurring in the puts from agricultural drainage will be- toplankton. Data collected by the USGS southern Delta during the extremely come a much more important issue. National Water-Quality Assessment dry El Niño–Southern Oscillation of program demonstrate that seven pesti- 1976 to 1977 (Jassby et al. 2002). Nutri- Ecosystem restoration cides in the San Joaquin River Basin fre- ent sources and this nutrient excess are The research described here high- quently exceed criteria for the protection not as pronounced downstream in San lights the importance of phytoplankton of aquatic life, and diazinon concentra- Francisco Bay, and nitrogen can become in sustaining the metazoan food web tions sometimes reach acutely toxic levels limiting during spring phytoplankton on a Delta-wide basis, despite the pres- in the San Joaquin River (Dubrovsky et blooms in the South Bay. ence of many other organic matter al. 1998). Similarly, diazinon and Excessive nutrients from agricultural sources. Organic matter in agricultural chlorpyrifos are linked to toxicity in drainage or animal wastewater have pro- drainage is mostly in dissolved form test zooplankton in the Sacramento moted huge and harmful phytoplankton and not an important nutrient or en- River watershed. The Regional Moni- blooms in many locations around the ergy source for the metazoan food web; toring Program of the San Francisco world (Anderson et al. 2002). This is not a along with phytoplankton and other Estuary Institute has established that major problem in the Delta currently be- sources, however, it reacts with disin- these organophosphate pesticides are cause of high concentrations of sus- fectants during drinking-water treat- also of concern in San Francisco Bay. pended sediments and accompanying ment to form potentially harmful While there is a growing body of infor- turbidity. High turbidity is in part a byproducts. Phytoplankton biomass —

108 CALIFORNIA AGRICULTURE, VOLUME 57, NUMBER 4 and therefore the food supply for cuses on environmental quality to “im- Anderson DM, Glibert PM, Burkholder higher organisms — has declined over prove and increase aquatic and terres- JM. 2002. Harmful algal blooms and eutrophication: Nutrient sources, composi- the past few decades, partly because of trial habitats and improve ecological tion and consequences. Estuaries 25:704–26. the Asian clam invasion. Certain herbi- functions in the Bay-Delta to support Bennett WA, Moyle PB. 1996. Where cides in agricultural drainage may at sustainable populations of diverse and have all the fishes gone? Interactive factors producing fish declines in the Sacramento- times inhibit phytoplankton produc- valuable plant and animal species” San Joaquin estuary. In: Hollibaugh JT (ed.). tion, especially in winter, but their (CALFED 2000). This is one of the larg- San Francisco Bay: The Ecosystem. San Fran- overall effect on annual production is est attempts at ecosystem restoration cisco: Pacific Division, AAAS, California probably limited. Similarly, certain pes- worldwide, with a multibillion dollar Academy of Sciences. p 519–42. Bull RJ, Kopfler FC. 1991. Health effects ticides can reach toxic levels for pri- budget and a period of 25 to 30 years of disinfectants and disinfection by-products. mary consumers of phytoplankton, but for full implementation. Addressing the AWWA Research Foundation and American any ecological significance has not yet decline in system productivity is part of Water Works Association, Denver, CO. been demonstrated. one of the key strategic goals of this CALFED. 2000. Executive summary, final programmatic Environmental Impact State- The phytoplankton decline may rep- ecosystem restoration. ment/Environmental Impact Report. CALFED resent a reduction in the system’s ca- Attainment of the CALFED Bay- Bay-Delta Program, Sacramento, CA. pacity to support higher levels of the Delta Program restoration goals re- Dubrovsky NM, Kratzer CR, Brown LR, et al. 1998. Water quality in the San Joaquin- food web. Lower phytoplankton levels quires a solid base of scientific Tulare Basins, California, 1992–1995. Circular have been linked to declines in key understanding to identify key ecosys- 1159, US Geological Survey, Denver, CO. zooplankton populations in the Delta. tem functions within the Delta and to Edmunds JL, Kuivila KM, Cole BE, Cloern Although the evidence for food limita- describe how they change in response JE. 1999. Do herbicides impair phytoplankton primary production in the Sacramento- tion of fish populations is not as strong to human activities, including restora- San Joaquin River Delta? In: Morganwalp as for zooplankton and benthic inverte- tion actions. Restoration actions — in- DW, Buxton HT (eds.). US Geological Survey brates, data from many estuaries and cluding new canals, flow and fish Toxic Substances Hydrology Program, Proc other water bodies also points to an barriers, increased use of floodplains Tech Meeting, Charleston, SC, March 8–12, 1999. Vol. 2. Contamination of Hydrologic overall correspondence between fish and increased shallow-water habitat — Systems and Related Ecosystems. US Geo- production and primary production all have significant impacts on phyto- logical Survey Water Resources Investigation (Nixon and Buckley 2002). Unless phy- plankton production, some positive Report 99-4018B. p 81–8. Jassby AD, Cloern JE. 2000. Organic toplankton productivity increases, res- and some negative (Jassby and Cloern matter sources and rehabilitation of the toration of fish populations in the 2000). Given the significance of phyto- Sacramento-San Joaquin Delta (California, Bay-Delta may be limited. Water trans- plankton production to the food USA). Aquatic Conservation: Marine and parency has increased over the past few base in the Delta, as well as other Freshwater Ecosystems 10:323–52. Jassby AD, Cloern JE, Cole BE. 2002. An- decades due to declines in suspended phytoplankton-related functions, nual primary production: Patterns and mecha- sediments, enhancing phytoplankton these impacts must be defined nisms of change in a nutrient-rich tidal photosynthesis and partially offsetting quantitatively and used to help ecosystem. Limnol Oceanogr 47:698–712. consumption by clams. A continuation guide the restoration strategy. Miller J, Miller M, Larsen K, et al. 2002. Identification of Causes of Algal Toxicity in of the transparency trend could result Sacramento-San Joaquin Delta. Central Val- in increased phytoplankton production ley Regional Water Quality Control Board, because of the excess nutrients avail- Sacramento, CA. 29 p. A.D. Jassby is Research Ecologist, De- Müller-Solger AB, Jassby AD, Müller- able in the estuary from fertilizer runoff Navarra D. 2002. Nutritional value of par- and wastewater treatment effluent. Al- partment of Environmental Science and ticulate organic matter for zooplankton though this could have positive effects Policy, UC Davis; J.E. Cloern is Research (Daphnia) in a tidal freshwater system on overall fish production, there is a Biologist, Water Resources Division, (Sacramento-San Joaquin River Delta, USA). U.S. Geological Survey (USGS); and Limnol Oceanogr 47:1468–76. potential danger from nuisance and Nixon SW, Buckley BA. 2002. “A strik- harmful phytoplankton species that A.B. Müller-Solger is Environmental ingly rich zone”: Nutrient enrichment and pose both human and ecological toxic- Specialist, California Department of Water secondary production in coastal marine eco- ity problems. Resources. The authors are grateful for systems. Estuaries 25:782–96. Orsi JJ, Mecum WL. 1996. Food limitation As a response to symptoms of gross funding from CALFED (1425-98-AA-20- as the probable cause of a long-term decline ecosystem disturbance and the critical 16240), USGS and the U.S. Environmental in the abundance of Neomysis mercedis the role of the Delta as the linkage between Protection Agency (EPA) through the Cen- opossum shrimp in the Sacramento-San ter for Ecological Health Research at UC Joaquin Estuary. In: Hollibaugh JT (ed.). San San Francisco Bay and its watershed, a Francisco Bay: The Ecosystem. San Francisco: consortium of state and federal agen- Davis (R819658). Although EPA partially Pacific Division, AAAS, California Academy cies was established in 1994. The funded preparation of this article, it does not of Sciences. p 375–401. CALFED Bay-Delta Program’s mission necessarily reflect the views of the agency and Sobczak WV, Cloern JE, Jassby AD, no official endorsement should be inferred. Müller-Solger AB. 2002. Bioavailability of or- is to develop a long-term and compre- ganic matter in a highly disturbed estuary: hensive plan to “restore ecological The role of detrital and algal resources. Proc References health and improve water management Nat Ac Sci 99:8101–5. for the beneficial uses of the Bay-Delta Alpine AE, Cloern JE. 1992. Trophic inter- Wright SA, Schoellhamer DH. In press. actions and direct physical effects control Trends in the sediment yield of the Sacra- system.” The program is centered phytoplankton biomass and production in mento River, California, 1957–2001. SF Estu- around four objectives, one of which fo- an estuary. Limnol Oceanogr 37:946–55. ary Watershed Sci.

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