TMDL for Nutrients in Lower Salinas River Watershed, Monterey County, California

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A watershed-related issue examined by the ENVS 560/L Watershed Systems class at CSUMB.

Summary

The Salinas River Watershed, which includes the Nacimiento River, San Antonio River, Estrella River, and Arroyo Seco River, encompasses approximately 4,600 square miles within the Monterey Bay Region of California. The Lower Salinas River Watershed (LSRW) supplies water for many cities on California's Central Coast, from San Luis Obispo to Salinas (with their intensively farmed, productive agricultural valleys). The river flows into one of the world's most diverse marine ecosystems (CITE), Monterey Bay National Marine Sanctuary (MBNMS) at Moss Landing Harbor carrying pollutants acquired as it flows. The Salinas River is designated by the California State Water Resources Control Board (SWRCB) as one of the most critical watersheds in California due to degrading habitats and nonpoint source pollution impacts on water quality. Anthropogenic sources of nutrient loading to the Salinas River are a particular concern, given the high amount of agricultural land use within the LSRW.

Map of the Lower Salinas River Watershed (by Alberola 2011)

Nutrient TMDLs in the Lower Salinas Watershed

The Total Maximum Daily Load (TMDL) for Nutrients in the LSRW is determined by the Regional Water Quality Control Board Central Coast Region (CCRWQCB). The TMDL for nutrients for the LSRW has been in development for many years and a preliminary draft project report for the LSRW and the Moro Cojo Slough subwatershed was completed in 2012.

2010 TMDL Report

The CCRWQCB presented a progress report in June 2010 that contains background information, provisional nutrient targets, and a compilation of water quality data for water bodies in the region. The 2010 progress report identifies potential nutrient load sources. A draft source analysis portion of the TMDL project is available from the 2012 draft TMDL document[1] (UPDATE).

The 2010 303(d) list of Impaired Waterbodies is the current and active list for the California Central Coast. In 2010, the CCRWQCB presented an updated list in its 2010 Integrated Report, but this report has not yet been approved by the US EPA[2].

The TMDL progress report did not address 'critical' environmental factors associated with nutrient loading in the LSRW, in which a slight increase in nutrients could lead to exceedance of water quality objectives. However, the progress report does specify some indicators that can impair the beneficial uses of the regional water bodies.

Data analysis for the June 2010 California Regional Water Board Progress Report included:

  • A delineation of watershed boundaries
  • A list of subwatersheds
  • Stream classification, which revealed in general low gradient streams on the valley floor were perennial, and many headwater streams tended to be ephemeral
  • An assessment of groundwater as baseflow. For the TMDL project area baseflow index values for groundwater ranged from 38 to 26 percent
  • An assessment of mean groundwater nitrate concentrations for the project area. Values reported ranged from 0.1-10.0 mg/l to 100.1-200.0 mg/l of nitrate
  • An assessment of mean annual precipitation for the project area. For the project area values ranged between 11.1 inches to 33.5 inches on average annually
  • An analysis of land use and land cover. In the project area, land uses include approximately 34% farmland, 31% grazing land, 8% urban, and 26% undeveloped/forested/restricted

2012 TMDL Report

The 2012 CCRWQCB project report draft of TMDL for nutrients in the Lower Salinas River Watershed (LSRW) (Monterey County, CA)[1] is titled: Total Maximum Daily Loads for Nitrogen Compounds and Orthophosphate for the Lower Salinas River and Reclamation Canal Basin, and the Moro Cojo Slough Subwatershed, Monterey County, California AND WAS COMPLETED/FILLED DATE. Nutrients are defined as biologically-accessible nitrogen compounds and orthophosphate loading into waterways of the LSRW.

This draft report indicates a proposed geographic scope of around 405 acres in the Lower Salinas Valley of northern Monterey County, focused on the two major drainages, the Reclamation Canal Drainage and the Lower Salinas River Drainage (pictured at right). The Moro Cojo subwatershed is identified as a subwatershed in the report.

The ultimate receiving body (drainage) of both waterways and tributaries is the Monterey Bay and the Monterey Bay National Marine Sanctuary. Pollutants addressed by the proposed 2012 TMDL draft are nitrate, un-ionized ammonia, and orthophosphate. Reductions in pollutants are expected to target 303(d)-listed impairments from low dissolved oxygen (DO) and chlorophyll-a within the project area. These impairments relate to the biostimulatory effects of nitrate and orthophosphate on freshwater systems.

According to the draft TMDL report (2012):

"Discharges of nitrogen compounds and orthophosphate are occurring at levels in surface waters which are impairing a wide spectrum of beneficial uses and, therefore, constitute a serious water quality problem. The municipal and domestic drinking water supply (MUN, GWR) beneficial uses and the range of aquatic habitat beneficial uses are currently impaired; potential or future beneficial uses of the agricultural irrigation water supply (AGR) for sensitive crops may be impaired. A total of 34 waterbody/pollutant combinations are impaired due to exceedances of water quality objectives. The pollutants addressed in this TMDL are nitrate, un-ionized ammonia, and orthophosphate. Orthophosphate is included as a pollutant due to biostimulatory impairments of surface waters. Reducing these pollutants is also anticipated to address several 303(d)-listed dissolved oxygen and chlorophyll a impairments in the TMDL project area. As a result of these conditions, beneficial uses are not being protected." and
"By developing TMDLs for the aforementioned pollutants, the water quality standards violations being addressed in this TMDL include:

  • Violations of drinking water standard for nitrate
  • Violations of the Basin Plan general toxicity objective for inland surface waters and estuaries (violations of un-ionized ammonia objective)
  • Violations of the Basin Plan narrative general objective for biostimulatory substances in inland surface waters and estuaries (as expressed by excessive nutrients, chlorophyll a, algal biomass, and low dissolved oxygen)"


According to the CCWRQCB draft TMDL nutrient report (2012):

"There does not appear to be a significant geologic reservoir in the project area that could contribute to elevated nitrogen loads to surface waters."

Eutrophication of waterways may occur when excess nutrients are present and environmental conditions promote algal growth. Biologically-accessible nitrogen and phosphorus are limiting nutrients in many ecosystems (CITE). In general, sources of nutrients in watersheds include: urban runoff, fertilizers, groundwater, livestock, wastewater treatment plants, and septic systems. Specifically for the Lower Salinas River Watershed (Anderson et al. 2003) [3] identified irrigated agriculture as the dominant source of nutrients in watersheds in the region.

According to the SWRCB-contracted UC Davis report[4] (Harter and Lund 2012) on nitrate in California's Drinking Water for the State Water Resources Control Board (SWRCB), nitrates are reducing quality of drinking water from shallow wells. The report concludes that: "Most nitrate in drinking water wells today was applied to the surface decades ago."

The report is part of a contracted study for the SWRCB as part of the Senate-mandated Groundwater Nitrate Project as part of biannual reporting on initial studies into nitrate effects on drinking water in the Tulare Basin and Salinas Valley. The report also cites agriculture as the estimated source of 96% of nitrate loading to groundwater--200 Gg/yr (1 Gg = 1100 tons) within these regions, with the next largest (estimated) source (wastewater treatment and food processing wastes) loading 3.2 Gg nitrate/yr to groundwater.

Map of major drainages in the nutrient TMDL draft (2012) for the Lower Salinas River Watershed[1].
Latest map of impaired (303(d) listed) waterways of the Lower Salinas River Watershed) (2010)

Nutrient Pollutants in the Lower Salinas Watershed

Nutrient pollutants are of concern because of direct and indirect effects on freshwater aquatic habitats and groundwater stores.

Information on the implementation and monitoring can be found here: Lower Salinas River Watershed Nutrient TMDL - Implementation and Monitoring Progress.

The June 2010 California Regional Water Board Nutrient TMDL Progress Report acknowledges that the presence of excess nutrients does not directly impair waterways, rather, indirect impacts associated with the presence of excess nutrients diminish beneficial uses of waterways.

Secondary indicators of eutrophication ("biostimulation") such as nuisance algal blooms, drastic diel swings in dissolved oxygen concentrations, and loss of habitat must also be monitored and documented as they are more directly linked to the beneficial uses of waterways than nutrient concentrations alone.

Numeric Targets

The CCRWQCB issued a TMDL concise tabular summary in 2013. The summary clearly identifies numeric targets for Nitrate as N, orthophosphate as P, and un-ionized ammonia as N during the Dry season, Wet season and Year round. The numeric targets are as follows:

Dry Season (May 1 - Oct 31): Nitrate as N: must not exceed 1.4 to 6.4 mg/L in impaired receiving waters, depending on specific stream reach. Orthophosphate as P: must not exceed 0.7 to 0.13 mg/L in impaired recieving waters, depending on specific stream reach.

Wet Season (Nov 1 - Apr 30): Nitrate as N: must not exceed 8 mg/L in impaired receiving waters, depending on specific stream reach. Orthophosphate as P: must not exceed 0.3 mg/L in impaired recieving waters, depending on specific stream reach.

Year Round: Nitrate as N: must not exceed 10 mg/L in all recieving water designated MUN Un-ionized ammonia as N: must not exceed 0.025 mg/L in all receiving waters

The progress report described that one uniform nutrient target may not be sufficient in light of the large variability of stream morphology and hydraulics in the waterbodies contributing to the Lower Salinas River. The report explored a variety of ways to define a range of numeric targets. Final nutrient targets can be developed based on either calculations or estimations. The percentile based approach calculates the numeric target by using either the 25th percentile of nutrient data from reference streams or the 75th percentile of all nutrient data for the project area streams. The nutrient numeric endpoints (NNE) approach estimates in-stream benthic algal response to ambient stream conditions.

Based on these approaches, the provisional and preliminary numeric targets for total nitrogen listed in the progress report range from 1.4-2.2 mg/L depending on waterbody type.

Photographic documentation of waterways with high eutrophication (biostimulation) in the Lower Salinas River Watershed (from 2012 TMDL draft report)

Source Analysis

A draft source analysis for nutrients in the Lower Salinas River watershed has not been completed as of March 2016. The report uses STEPL (Spreadsheet Tool for Estimating Pollutant Load) to calculate nutrient loads (nitrogen and phosphorus--N and P) from various characteristics including watershed area, and nutrient loads (based on land use and land cover--LULC). These estimates are made at the project-area scale (405 acres), and can be recalculated for individual subwatersheds. The report cites a 1999 US EPA report and states, "both nitrogen and phosphorus reach surface waters at an elevated rate as a result of human activities."

This analysis reports estimates for urban annual N Load (lb/yr) and P Load (lb/yr) at 138,391 and 21,796 respectively.

Cropland estimates of N and P loading at 2,211,230 and 629,492 lbs/year by far made up the greatest proportion of source loads identified in the project area. Total N and P loading (lbs/year) were 2,911,676 and 793,236 respectively. This means that agriculture represents 76% of N and 79% of P loading in the area.

Grazing (209,521; 123,412) and forest (27,649; 11,327) also make contributions as well.

Because shallow groundwater acts as a reservoir for elevated concentrations of nitrogen and phosphorus in the region[4], their contribution to baseflow in streams becomes a prominent source of surface water nutrients in the dry (summer) season. These groundwater to surface water nutrient additions amount to 323,957 and 6,985 lbs/year nitrogen and phosphorus loading, respectively. Citing the Tetratech (2003) reporting (CITE), the draft TMDL report (2012) notes:
"...groundwater loads appear to be overwhelmingly due to human influences on groundwater in the project area."

Atmospheric deposition made up a less proportionate impact on N and P loading, however, it may have a disproportionate impact in terms of nutrient loading on lakes and reservoirs due to their high surface area. Atmospheric deposition annual load (lbs./year) were 899 and 211, respectively.

There is a preliminary source analysis prepared by Anderson, et al. (2003) that identified irrigated agriculture as a dominant source for high nutrient concentrations in southern Monterey Bay watersheds. The report notes that the source assignment is strongly qualitatively suggested "through "overwhelming" correlation of nutrient concentration data and land use."

A study by the Lawrence Livermore National Laboratory (CITE Moran et al. 2011) demonstrated concurrent results, based of geochemical and isotopic signatures pointing to irrigated agriculture as the largest source of nitrate to surface and groundwater in areas sampled of the Salinas Valley. Specifically, isotopic signatures of oxygen matched inorganic fertilizers, and not those ranges expected from animal waste. The 2012 TMDL draft report acknowledges limitations in the geographic scope of the 2011 LLNL study in not being extrapolated to areas of the LSRW, while pointing out the utility of the study in backing, " ...the mass balance-based source analysis developed in this TMDL project report." Importantly, this study contrasts with Harter-Lund contract report for the SWRCB (2012) which states that the nitrate found in shallow groundwater comes from nutrient applications from decades ago (dairy waste or animal manure application).


Monitoring

The Environmental Protection Agency Nutrient TMDL development protocol document (2000) [5] suggested steps include:

  • identifying key questions
  • evaluating monitoring options and
  • implementing the monitoring program.


Irrigated agriculture has been identified as the dominant nutrient source contribution to the Lower Salinas River Watershed. As such, the monitoring plan for the LSRW necessarily focuses on quantifying agricultural nutrient source analysis. Monitoring may be informed by requirements outlined in the Ag Waiver evaluating results to ensure that agricultural best management practices (BMPs) are adequate to reduce nutrient levels.

Urban stormwater runoff is another important source of nutrients in the LSRW. As the City of Salinas has already implemented a Storm Water Monitoring Program water board staff should evaluate their results to ensure the Storm Water Management Program is effective at reducing nutrient effluent and has implemented Best Management Practices.

The MOS for the Lower Salinas River Watershed is dependent on the assumptions put into the INN benthic biomass modeler.

In establishing TMDL allocations in the Lower Salinas River Watershed for nutrients, the Regional Water Quality Control Board could approach the allocations in a similar fashion as that taken in the Pajaro River Nitrate TMDL. By setting the load allocations as a concentration at or below the numeric target for all sources, future growth and changes in land use will not lead to an exceedance of the TMDL. This will also eliminate the need for setting critical conditions based on changes in flow rate, which would absolutely be required if allocations were set as loads given in mass.

The following table details impaired water bodies within the Salinas Watershed, and the justification for nutrient-related listing in the 2006, 2010, and 2012 impairment list. The list comprises 20 listed waterbodies with a combined six sources of impairment.

Monitoring information can be found here: Lower Salinas River Watershed Nutrient TMDL - Implementation and Monitoring Progress


(No data reported past March 2010)

Water Body 2006 Listed Impairment 2010 Listed Impairment 2012 Listed Impairment
Alisal Creek Nutrient Chlorophyll-a, Nitrate Ammonia (Un-ionized), Chlorophyll-a
Alisal Slough Not Listed Low Dissolved Oxygen, Nitrate Low Dissolved Oxygen, Nitrate (biostimulatory*)
Blanco Drain Not Listed Low Dissolved Oxygen, Nitrate Low Dissolved Oxygen, Nitrate (biostimulatory)
Chualar Creek Not Listed Ammonia (Un-ionized), Nitrate Nitrate (drinking water)
Esperanza Creek Not Listed Nitrate Nitrate (drinking water), (NO DATA on un-ionized ammonia)
Espinosa Slough Not Listed Ammonia (Un-ionized), Nitrate Ammonia (Un-ionized), Nitrate (drinking water)
Gabilan Creek Nitrate Ammonia (Un-ionized), Nitrate Nitrate (drinking water)
Lower Reclamation Canal N/A N/A Ammonia (Un-ionized), Low Dissolved Oxygen, Nitrate (biostimulatory)
Lower Salinas River N/A N/A Nitrate (biostimulatory)
Merrit Ditch Not Listed Ammonia (Un-ionized), Low Dissolved Oxygen, Nitrate Ammonia (Un-ionized), Low Dissolved Oxygen, Nitrate (biostimulatory)
Moro Cojo Slough Ammonia (Un-ionized), Low Dissolved Oxygen Ammonia (Un-ionized), Low Dissolved Oxygen Ammonia (Un-ionized), Low Dissolved Oxygen
Natividad Creek Nitrate Ammonia (Un-ionized), Low Dissolved Oxygen Ammonia (Un-ionized), Low Dissolved Oxygen, Nitrate (biostimulatory)
Old Salinas River Not Listed Chlorophyll-a, Low Dissolved Oxygen, Nitrate Chlorophyll-a, Low Dissolved Oxygen, Nitrate (biostimulatory)
Old Salinas River Estuary Ammonia (Un-ionized), Low Dissolved Oxygen, Nutrients Nutrients N/A (not in 2012 report?)
Quail Creek Nutrients Ammonia (Un-ionized), Low Dissolved Oxygen, Nitrate Ammonia (Un-ionized), Nitrate (drinking water)
Salinas Reclamation Canal Ammonia (Un-ionized), Low Dissolved Oxygen Ammonia (Un-ionized), Low Dissolved Oxygen, Nitrate Ammonia (Un-ionized), Low Dissolved Oxygen, Nitrate (biostimulatory)
Salinas River (lower, estuary near Gonzales Rd. Crossing) Nitrate, Nutrients Nitrate Nitrate (biostimulatory)
Salinas River Lagoon (North) Nutrients Nutrients N/A (not in 2012 report?)
Santa Rita Creek Nitrate Ammonia (Un-ionized), Low Dissolved Oxygen, Nitrate Ammonia (Un-ionized), Low Dissolved Oxygen, Nitrate (drinking water)
Tembladero Slough Ammonia (Un-ionized), Nutrients** Chlorophyll-a, Nitrate, Nutrients** Chlorophyll-a, Nitrate (biostimulatory), Nutrients
  • Nitrate is divided into biostimulatory impairment concentrations and drinking water impairment concentrations of 1.7-6.4 and 10 mg/L respectively.
    • Nutrient impairment refers to the biostimulatory effects of orthophosphate on algal bloom impairment.

Nitrate example

Surface nitrate concentrations and estimated source contributions in the LSRW.

The project report completed in March 2013 by the California Regional Water Quality Control Board, (CRWQCB) Central Coast Region (CCRWQCB) on TMDLs for nutrients in the Lower Salinas River Watershed[6] Link to Waterboard TMDLs for Nutrients in the Lower Salinas Watershed [5]</ref>.

In this document, the work group identifies multiple beneficial uses (BUs) as impaired, including those for drinking water supply, livestock watering, and aquatic habitat BUs.

From the 2013 project report[6]:

"Problem Statement: "Discharges of nitrogen compounds and orthophosphate are occurring at levels in surface waters which are impairing a wide spectrum of beneficial uses and, therefore, constitute a serious water quality problem. The municipal and domestic drinking water supply (MUN, GWR) beneficial uses and the range of aquatic habitat beneficial uses are currently impaired; potential or future beneficial uses of the agricultural irrigation water supply (AGR) for sensitive crops may be impaired..."

"A total of 34 waterbody/pollutant combinations are impaired due to exceedances of water quality objectives. The pollutants addressed in this TMDL are nitrate, un-ionized ammonia, and orthophosphate – orthophosphate is included as a pollutant due to biostimulatory impairments of surface waters. Reducing these pollutants is also anticipated to address several 303(d)-listed dissolved oxygen and chlorophyll a impairments in the TMDL project area."

Beneficial Uses (BUs) Associated with Waterways Listed for Nutrient Impairments

Beneficial uses of waterways and water quality objectives are vital to determining water quality standards and goals. Below is a list of BUs, and a table showing identified BUs for water bodies within the Salinas watershed.

  • Municipal and Domestic supply (MUN)
  • Agriculture (AGR)
  • Industrial Process (PRO)
  • Industrial Service (IND)
  • Ground Water Recharge (GWR)
  • Water Contact Recreation (REC1)
  • Non-Contact Water Recreation (REC2)
  • Cold Freshwater Habitat (COLD)
  • Warm Freshwater Habitat (WARM)
  • Estuarine Habitat (EST)
  • Wildlife Habitat (WILD)
  • Rare, Threatened, or Endangered Species (RARE)
  • Migration of Aquatic Organisms (MIGR)
  • Spawning, Reproduction, and/or Early Development (SPWN)
  • Biological Habitats of Special Significance (BIOL)
  • Shellfish Harvesting (SHELL)
  • Commercial and Sport Fishing (COMM)
  • Freshwater replenishment (FRESH)
Waterbody MUN AGR PRO IND GWR REC1 REC2 WILD COLD WARM MIGR SPWN BIOL RARE EST FRESH COMM SHELL
Old Salinas River Estuary X X X X X X X X X X X X
Salinas River Lagoon (North) X X X X X X X X X X X X
Tembladero Slough X X X X X X X X X
Espinosa Slough X X X X X
Salinas Reclamation Canal X X X X X
Alisal Creek X X X X X X X X X X
Blanco Drain X X X X X
Salinas River, down stream of Spreckels Gage X X X X X X X X X
Salinas River,Chualar to Spreckles X X X X X X X X X X X X
Quail Creek X X X X

Public Participation

Due to the large number of stakeholders that are affected by the implementation of Lower Salinas River Watershed Nutrient TMDL, the Central Coast Water board had scheduled various public hearings and collaborative stakeholder meetings during different stages of the process.

During the development of the Fecal Coliform TMDL report for the Lower Salinas River Watershed (2010 Report), Water Board staff conducted stakeholder outreach efforts throughout the process. Water Board staff made several presentations to engage stakeholders and results were presented in newspapers and television media. In addition, a CEQA stakeholder scoping meeting was held in June of 2007 and another stakeholder meeting was held in August of 2009. A formal Central Coast Water Board public hearing was also held and public comments were solicited prior to the hearing.

Stakeholders included:

References

  1. 1.0 1.1 1.2 Link to Central Coast Water Quality Control Board's draft TMDLs for Nutrients in the Lower Salinas Watershed [1]
  2. SWRCB list of US EPA approved and effective TMDLs for California [2]
  3. Anderson T, Watson F, Newman W, Hager J, Kozlowski D, Casagrande J, Larson J. 2003. Nutrients in surface waters of the southern Monterey Bay watersheds. Central Coast Watershed Studies
  4. 4.0 4.1 UC Davis contract study report on the Tulare Valley and Lower Salinas Watershed addressing nitrates in the California's drinking water [3]
  5. [4]
  6. 6.0 6.1 LSRW Nutrient TMDL Staff Report

See also

External Links

Disclaimer

This page may contain student work completed as part of assigned coursework. It may not be accurate. It does not necessary reflect the opinion or policy of CSUMB, its staff, or students.