POD Archive Data

Project Summary:

January 1, 2006 – April 30, 2010 Funding Agency: Interagency Ecological Program, Sacramento, CA Principal Investigator: Inge Werner, Aquatic Toxicology Laboratory, Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, UC Davis, CA

In the last several years, abundance indices of numerous pelagic fish species residing in the Sacramento-San Joaquin Delta of California, USA, have shown marked declines and record lows for the endemic delta smelt (Hypomesus transpacificus), age-0 striped bass (Morone saxatilis), longfin smelt (Spirinchus thaleichthys) and threadfin shad (Dorosoma petenense).While several of these species - including in particular longfin smelt and juvenile striped bass - have shown evidence of long-term declines, there appears to have been a precipitous “step-change” to very low abundance during the period 2002-2004. It is presently unclear what might have caused this critical population decline, but toxic contaminants may be one of several factors acting individually or in concert to lower pelagic productivity.

The goal of this study is to assess the potential for contaminated water to contribute to the observed declines of pelagic species in the Delta, and consists of the following elements:

Toxicity Testing: The study design is building on results of a 2005 pilot project to investigate toxicity of Delta water samples to invertebrates and early life stages of fish species of concern. In 2008-10, toxicity testing is intensified in some important areas (Cache Slough/lower Sacramento, Suisun Marsh and Bay) of the Delta where acute toxicity was detected in 2007, as well as the south-eastern Delta. When acute toxicity (>=50% mortality within 7 d) to the amphipod Hyalella azteca is detected, toxicity identification evaluations and chemical analysis are used to identify toxicant(s). If a sample causes >=50% mortality within 96 h, follow-up samples are collected in an attempt to identify the sources of toxicity.

In situ tests with fish (delta smelt, possibly striped bass, fathead minnow or inland silverside) and invertebrates (Hyalella azteca) will be conducted at suitable locations (Hood, Rough & Ready Island) to expose test species to water in the field and integrate potential water toxicity over time. In addition, laboratory toxicity tests with larval delta smelt will be performed in late April-June on water samples from four select locations of special concern such as Cache Slough, lower Sacramento and San Joaquin Rivers, Suisun Marsh.

Species Sensitivity Studies: Presently, the overwhelming lack of information on the toxic effects of contaminants on resident Delta species, among them delta smelt and two important prey species, Pseudodiaptomus forbesi and Eurytemora affinis, prevents an estimation of the risk of chemical contamination to pelagic organisms of concern. There is an urgent need for information on their sensitivity to toxic chemicals relative to standard test species. This study will generate such sensitivity data (in the form of 96-h LC50, EC50, no observed effect level (NOEC), and lowest observed effect level (LOEC)) and compare sensitivity of Delta species with that of standard toxicity test species. Chemicals were selected based on their known presence in the Delta, recent past or present. Suggested candidates are copper, ammonia, the organophosphate insecticides chlorpyrifos and diazinon, and the pyrethroid insecticides, cyfluthrin, bifenthrin, permethrin and lambda-cyhalothrin.

Molecular Field Biomarkers for Species of Concern: Changes in the gene transcription of stress response genes in resident fish can be powerful biomarkers for the identification of sublethal impacts of environmental stressors on aquatic ecosystems. Molecular biomarkers were developed for striped bass in 2006-07. A microarray was developed for delta smelt, and biomarker development continues with the immediate aim of selecting appropriate biomarkers for use in field and in situ studies, as well as in laboratory studies to determine cause and effect, and to link cellular biomarker responses to ecologically relevant effects such as swimming ability, growth and survival. As soon as molecular biomarkers for delta smelt are available, archived tissue samples from laboratory and in situ exposures will be analyzed.

Questions Addressed:
1) Is water in ecologically sensitive areas of the Delta toxic to delta smelt and other pelagic fish and their prey?
2) What are the causes and sources of water column toxicity in areas of the Delta important for fish species of concern?
3) How sensitive are Delta species to contaminants in comparison to surrogate species commonly used in toxicity testing? Is it meaningful to use surrogate species for toxicity monitoring in the Delta?
4) Are contaminants associated with wastewater treatment effluents affecting fish species of concern?
5) Is there a relationship between toxicity results and other POD study components such as histopathologic examinantion of fish and Microcystis blooms?