Riverine Nutrient Trends in the Sacramento and San Joaquin Basins, California
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Peer Reviewed Title: Riverine Nutrient Trends in the Sacramento and San Joaquin Basins, California: A Comparison to State and Regional Water Quality Policies Journal Issue: San Francisco Estuary and Watershed Science, 13(4) Author: Schlegel, Brandon, California State University, Sacramento Domagalski, Joseph L., U.S Geological Survey, California Water Science Center Publication Date: 2015 Permalink: http://escholarship.org/uc/item/4c37m6vz Keywords: Sacramento–San Joaquin River Delta, nutrients, nitrogen, phosphorus, nutrient transport, nutrient loads, agricultural drainage Local Identifier: jmie_sfews_29499 Abstract: doi: http://dx.doi.org/1015447/sfews.2015v13iss4art2 Non-point source (NPS) contaminant control strategies were initiated in California in the late 1980s under the authority of the State Porter–Cologne Act and eventually for the development of total maximum daily load (TMDL) plans, under the federal Clean Water Act. Most of the NPS TMDLs developed for California’s Central Valley (CV) region were related to pesticides, but not nutrients. Efforts to reduce pesticide loads and concentrations began in earnest around 1990. The NPS control strategies either encouraged or mandated the use of management practices (MPs). Although TMDLs were largely developed for pesticides, the resultant MPs might have affected the runoff of other potential contaminants (such as nutrients). This study evaluates the effect of agricultural NPS control strategies implemented in California’s CV before and between 1990 and 2013, on nutrients, by comparing trends in surface-water concentrations and loads. In general, use of MPs was encouraged during a “voluntary” period (1990 to 2004) and mandated during an “enforcement” period (2004 to 2013). Nutrient concentrations, loads, and trends were estimated by using a recently developed Weighted Regressions on Time, Discharge, and Season (WRTDS) model. Sufficient total phosphorus (TP), total nitrogen (TN), and nitrate (NO3) data were available to compare the voluntary and enforcement periods for twelve sites within the lower eScholarship provides open access, scholarly publishing services to the University of California and delivers a dynamic research platform to scholars worldwide. Sacramento and San Joaquin basins. Ammonia concentrations and fluxes were evaluated at a subset of these sites. For six of these sites, flow-normalized mean annual concentrations of TP or NO3 decreased at a faster rate during the enforcement period than during the voluntary period. Concentration changes during similar years and ranges of flow conditions suggest that MPs designed for pesticides may also have reduced nutrient loads. Results show that enforceable NPS policies, and accelerated MP implementation, limits NPS pollution, and may control runoff of non-targeted constituents such as nutrients. Supporting material: Appendix A: Fluxes for Selected Constituents in Water Years (October 1 to September 30) 1975-2013 Copyright Information: Copyright 2015 by the article author(s). This work is made available under the terms of the Creative Commons Attribution4.0 license, http://creativecommons.org/licenses/by/4.0/ eScholarship provides open access, scholarly publishing services to the University of California and delivers a dynamic research platform to scholars worldwide. DECEMBER 2015 Riverine Nutrient Trends in the Sacramento and San Joaquin Basins, California: A Comparison to State and Regional Water Quality Policies Brandon Schlegel*1 and Joseph L. Domagalski2 an “enforcement” period (2004 to 2013). Nutrient Volume 13, Issue 4 | Article 2 doi: http://dx.doi.org/10.15447/sfews.2015v13iss4art2 concentrations, loads, and trends were estimated by using a recently developed Weighted Regressions * Corresponding author: [email protected] 1 California State University, Sacramento, CA 95819 USA on Time, Discharge, and Season (WRTDS) model. 2 United States Geological Survey, California Water Science Center Sufficient total phosphorus (TP), total nitrogen (TN), Sacramento, CA 95819 USA and nitrate (NO3) data were available to compare the voluntary and enforcement periods for twelve ABSTRACT sites within the lower Sacramento and San Joaquin Non-point source (NPS) contaminant control strategies basins. Ammonia concentrations and fluxes were were initiated in California in the late 1980s under the evaluated at a subset of these sites. For six of these authority of the State Porter–Cologne Act and even- sites, flow-normalized mean annual concentrations tually for the development of total maximum daily of TP or NO3 decreased at a faster rate during the load (TMDL) plans, under the federal Clean Water Act. enforcement period than during the voluntary period. Most of the NPS TMDLs developed for California’s Concentration changes during similar years and Central Valley (CV) region were related to pesticides, ranges of flow conditions suggest that MPs designed but not nutrients. Efforts to reduce pesticide loads and for pesticides may also have reduced nutrient loads. concentrations began in earnest around 1990. The Results show that enforceable NPS policies, and NPS control strategies either encouraged or mandated accelerated MP implementation, limits NPS pollution, the use of management practices (MPs). Although and may control runoff of non-targeted constituents TMDLs were largely developed for pesticides, the such as nutrients. resultant MPs might have affected the runoff of other potential contaminants (such as nutrients). This KEY WORDS study evaluates the effect of agricultural NPS control strategies implemented in California’s CV before and Sacramento–San Joaquin River Delta, nutrients, between 1990 and 2013, on nutrients, by comparing nitrogen, phosphorus, nutrient transport, nutrient trends in surface-water concentrations and loads. In loads, agricultural drainage general, use of MPs was encouraged during a “vol- untary” period (1990 to 2004) and mandated during SAN FRANCISCO ESTUARY & WATERSHED SCIENCE VOLUME 13, ISSUE 4, ARTICLE 2 INTRODUCTION The goal of this investigation is to relate changes in California’s agricultural NPS control program The two largest rivers of the Central Valley of to the observed changes in nutrient concentrations California, the Sacramento and the San Joaquin, and loads in the Sacramento and San Joaquin river drain multiple land use types including extensive basins. To understand how nutrient concentra- mixed agriculture and urbanization (Figure 1). These tions and loads might have changed over time, we 2 two rivers collectively drain over 100,000 km of the used historical nutrient data to produce mass flux State of California, and are the primary sources of and concentration models for long-term monitoring fresh water to the Sacramento–San Joaquin Delta sites within the Sacramento and San Joaquin River (Delta). Over the years, numerous regulatory actions basins. We used flow-normalized trends in concentra- designated load reductions of various contaminants tions and loads to understand what effects, if any, of concern, mostly pesticides. There have also been California’s various agricultural non-point source changes in land use, cropping patterns, water man- (NPS) control programs, or other processes, might agement, and irrigation methodology, all of which have had. These programs have mostly been imple- may have had some effect on the transfer of vari- mented to control pesticide concentrations and asso- ous constituents from land to water and subsequent ciated toxicity. Like most other parts of the country, transport to the Bay–Delta system. Regulatory actions NPS control in California is achieved through the for pesticides resulted from 303(d) listings (http:// implementation of management (or conservation) www.waterboards.ca.gov/water_issues/programs/tmdl/ practices. Although agricultural NPS dischargers may integrated2010.shtml) of impaired water bodies as implement MPs for many reasons, pressures from a mandated by the Clean Water Act. Numerous stream regulatory body likely have the greatest effect. segments throughout the Central Valley have listings for various impairments. Although there have been This study examines key “turning points” in few listed impairments specifically for nutrients in California’s plan to control NPS pollution on nutrient the Central Valley, management practices (MPs) for trends in concentration and loads in the Sacramento other contaminants of concern and land use changes and San Joaquin river basins. We used these turning may have affected the loads of nutrients (nitrogen points to define time periods for trend analysis. The and phosphorus) entering the Delta from these the turning points refer to the incorporation of voluntary Sacramento and San Joaquin rivers over the last 2 or MPs and subsequent mandatory practices designed to more decades. reduce loads of specific constituents. Our goal was to understand in what direction, if any, nutrient concen- According to the 2010 Clean Water Act 303(d) list, trations or loads trend, and if those trends are related 51 out of 814 surface water bodies in the Central to time-periods of various management actions related Valley Region (Region 5 in California) are impaired to any type of NPS control. We do not examine any by nutrients (http://www.waterboards.ca.gov/water_ individual management practice or control program issues/programs/tmdl/integrated2010.shtml). Some in detail, but instead focus on analyzing how nutri- of those listings are for waterways of the Delta. Of ents have changed in these rivers and streams over