Examine the Christina River Project Part Two

Zinc Concentrations in Wetlands Compared to ERL and ERM

The distribution of zinc in sediment is compared to effects-based screening guidelines (Effects Range - Low(ERL), and Effects Range - Median,(ERM)). The map shows that zinc concentrations in wetland habitats along the main channel are probably toxic to benthic animals. (The red circles indicate concentrations above the ERM, a concentration that usually has a significant ecological impact.) Zinc was used to make paint at one of the NPL sites and was distributed up and down the river by tides. However, zinc concentrations are less than the ERM in the wetlands to the south of the main river channel. Zinc concentrations in tributaries are less than the ERL, a concentration below which toxic effects are seldom observed. Additional contaminants were evaluated in the same way.

Estuarine emergent wetlands usually have complete tidal exchange, and provide habitat where small fish can hide from predators. The riparian palustrine wetlands are likely to be former tidal wetlands that currently have a dike, tidegate, or other structure restricting tidal flows. These wetlands with impeded flow are good restoration candidates because they still contain wetland soils and propagules making regrowth of wetland vegetation relatively easy and inexpensive, once full tidal exchange is restored.

Anadromous Forage Fish Caught Near Wetlands of Interest

The GIS links fish survey results to the sampling stations shown on the map, indicating a few blueback herring and alewife were caught near the NPL sites. These small anadromous fish species provide food for larger fish and birds, and are a popular recreational catch. The project's goal is to increase the numbers of these two forage fish species.  Both these species are more successful in rivers that have riparian estuarine emergent wetlands.  Palustrine (non-tidal) emergent wetlands adjacent to the river can be converted to estuarine emergent wetlands by connecting them to the (tidal) river.  The image includes three types of wetlands: palustrine shrub/scrub, palustrine emergent, and estuarine emergent.

Land Use and Ecological Risk (Maximum ERM)

The map indicates the maximum probable toxicity at each sampling location, which was determined by taking the concentration of each measured contaminant (up to 25 per sample) and dividing by its median toxicity threshold (ERM). The highest ratio is mapped. In the wetlands along the old south channel, the ERM ratios do not predict toxicity, making these wetlands preferred for restoration projects. However, restoring tidal exchange may allow contaminants from the river to enter these wetlands.

Land use directly abutting the wetlands, and farther distant but within the watershed, can be checked for likely sources of future contamination. On the main channel, a large salvage yard is located on the river bank. Other potential contaminant sources are the airport, industrial, mixed urban uses, other urban build-up and highways. The map shows a vegetated buffer between most potential contaminant sources and the candidate wetlands. The proximity of the wetlands to the highway and the airport suggests that land in this area probably is less desirable for residential development, and therefore, relatively inexpensive to purchase for restoration.