Where is the final paper, y'all?
Audrey Ragsac
Nicholas Hu
Audrey Ragsac
Nicholas Hu
Discussion:
I. Amphipods, Isopods, and Odonata: Although the environment is variable, there are clear trends in community makeup across the salinity gradient. This is particularly pronounced in Amphipoda, Annelida and Isopoda, each of which reached an average of 50% of the sample composition at at least one site. All three orders contain both freshwater and marine species, making it difficult to say whether or not they are living at the edge of their respective fundamental niches.
The amphipods were best represented throughout the gradient, but their proportional representation declined significantly from site 1 to site 3 and again from site 5 to site 7 as the average seawater inundation time fell off. This appears to support the hypothesis that these amphipods are typically marine organisms living near the edge of their tolerance.
This regression shows that fluctuations in percent inundation have large effects on amphipod and odonata distributions in Cerrito Creek. Their numbers are larger in times of higher salinity. As salinity drops, their numbers decrease and begin to level off. Once the tide goes out far enough, amphipod and odonata numbers drop very quickly. Conversely, the middle R2 value for isopods most likely represents a high tolerance for large salinity fluctuations. Instead of following a strictly logistic pattern, the regression for this relationship decreases steadily at a fairly even rate. This suggests that factors other than salinity must affect isopod composition.
Factors that we were unable to consider in this study were species associated with each taxonomic order and the chemical composition of water and sediment. While we found significant trends involving taxonomic order, it would have been interesting to see if trends regarding specific species exist. Furthermore, chemical composition of water and sediment could have given a better understanding of the significance of variables we tested (pH and salinity). Any inconsistencies in data could have been due to human error in the sampling process. We went through each sample very thoroughly, but it is likely that some macroinvertebrates were missed due to their small size.
We found no Ephemeroptera, Plecoptera or Tricoptera, which are sensitive taxa commonly used in freshwater bioassessments. Odonata, which is moderately tolerant to salt water and metals, (Chessman and McEvoy 1998,Tollett et al. 2009) was the only aquatic insect larva that we found. It was present only at the three sites with the least exposure to seawater. Site 5, the most saline site at which Odonata was found, is inundated with seawater 31% of the time, which could point to a significant salinity tolerance. Because we only found two individuals at any one site, this evidence is anecdotal and the insects could simply have been washed downstream by the current.
II. Potential For Restoration: Our survey of the creek can be used as a persuasive factor for habitat restoration. In a comparative study conducted on Baxter Creek (another urbanized creek in El Cerrito, CA), restoration projects on one section of the creek showed greater taxa richness than sections without restoration projections (Purcell, et al. 2002). Similar to our methods, they used a net to loosen substrate and collect macroinvertebrates. By comparing samples of benthic macroinvertebrates from the restored site to an upstream un-restored site, they found that taxa richness was higher in the restored site. Thus, habitat quality improved in the restored section of the creek.
A 2001 sediment study of Cerrito Creek showed high PCB (Polychlorinated biphenyls) and mercury levels. PCB was present at 63 ppb and mercury at 340 ppb (Bell, et al, 2001). The accumulation of these toxins comes as no surprise, as a large portion of the creek was covered with cement during this time. Some locals were not even aware that a creek existed beneath the concrete, and many believed it to be a storm drain (Purcell, et al. 2002). However, despite the lack of public awareness, the Cerrito Creek Restoration Project day-lighted a section of the creek in 2003. The section was approximately 700 feet long and located between Talbot and Kains Streets, sandwiched between the El Cerrito Plaza parking lot and an apartment complex. (Berndt, et al. 2005). While this section of the creek was dramatically narrowed by the encroachment of urbanization and construction, there were still investments into restoring the state of the creek. As a part of the shopping center's renewal plan, the owner of the neighboring center agreed to move back their parking lot by 20 feet. The City of El Cerrito, the Friends of Five Creeks (a non-profit organization), and two companies collaborated to design a "natural meandering channel" that would lead to other goals, such as reducing the chance of flooding and bank erosion. The success of this restoration project is an example of how bioassessments and collaboration can improve the value and state of urban streams. Large parts of Cerrito Creek are engineered into channels or underground culverts (Berndt, et al. 2005). By re-introducing the creek to sunlight and open air, its natural ecosystem can be somewhat restored.
Moreover, a natural creek plays a unique role in an urban setting. In our study, as we move away from the mouth, Cerrito Creek moves into a heavily urbanized area, neighbored by Pacific East Mall, apartment complexes, and Albany Hill Park. The Creek adds aesthetic appeal to this area, where it extends past the mall parking lot into a more natural setting. This type of appeal is important in attracting and maintaining attention from the Creek's neighbors. While urban creeks are at high risk of being disturbed by human activity, they also are ideal areas to pursue restoration projects. Our study, as well as Purcell's study, is a good example of how small-scale restoration projects can be easily employed and repeated. Stream bioassessments are inexpensive and relatively simple to teach to volunteers. Creek restoration projects can be headed by volunteers, volunteer-based organizations, creek neighbors, or park visitors. Furthermore, our basic methods can be used to consistently monitor urban creeks and ensure that restoration projects are continuing in its order. Many restoration projects run into problems with maintaining previous efforts. In teaching volunteers about restoration and rehabilitation, they can become more aware of Cerrito Creek and their surroundings, which is an increasing topic of interest in urban environmentalism.
III. Future Studies: One factor that needs to be studied more extensively are the effects of invasive species in Bay Area wetland ecosystems. A Polish study on alien amphipod versus native amphipod distribution found that native amphipods find refugia in small rivers due to low conductivity, which is a rough estimate of salinity. Conversely, alien amphipods thrive in large rivers with higher conductivity. If salinity levels are elevated in small rivers due to improper sewage treatment or excessive runoff, there is a possibility of native amphipod extinction followed by alien species domination (Grabowski et al, 2009). While this is a European study, these findings are relevant to Bay Area wetlands because they are frequently exposed to many forms of pollution.
Invasive plants also have a large influence on benthic macroinvertebrate communities. Thirty years ago, San Francisco Bay was invaded by a species of hybrid cordgrass called Spartina. This species is outcompeting native grass species, which is expected to have adverse effects on physical and chemical processes in sediment habitats. A study of different stages of Spartina invasion along an elevation gradient showed that invasion is accompanied by a reduction in species richness and an increase in microalgal and Spartina feeder dominance (Neira et al, 2005). If Spartina composition continues to rise, then salinity gradients may cease to exist due to the formation of a bottom-up trophic cascade.
IV. Changes in Government Policy: In 2000, the European Union enacted the European Water Framework Directive. There are multiple parts to this directive, including coordination in international river basin districts, identifying and assessing water bodies at risk, proper groundwater management, proper management of artificial and modified water bodies, assessing water's economic value, implementation of water monitoring programs, water contaminant reduction, linking all European water legislation within a single framework, and public participation in water basin management planning (Directive 2000/60/EC). Although this is a relatively young directive, volumes of European wetland studies have emerged as products of its objectives.
In the United States, the 1972 Federal Clean Water Act is the main force in the protection of wetland and riparian areas. The act includes protection requirements for state water quality standards, including setting wastewater standards for industry (Summary of the Clean Water Act). Yet, while most protection is done at a federal level, no single framework linking all states exists. Furthermore, the Clean Water Act does not include as many criteria as the European Water Framework Directive. The Clean Water Act must be modified to include more criteria for wetland protection across many disciplines. Throughout this study, we observed much litter and many sources of pollution in and around Cerrito Creek. Therefore, we saw weaknesses of the Clean Water Act firsthand. We believe that our study can be used to further understand dynamics of wetlands in relation to city and regional planning.
Figure 5: Logistic regressions are shown
when percent inundation is compared to average percent compositions of
amphipods, isopods, and odonates.
The regression analysis for the relationships between the average percent composition of the orders amphipoda, odonata, and isopoda and percent inundation show a logistic pattern. The relationships between the average percent composition of amphipods and odonata and percent inundation are particularly strong, with R2 values of 0.94262 and 0.94262, respectively (See Figure 5). However, the R2 value for the relationship between average percent composition of isopods and percent inundation is much lower with a R2 value of 0.44447. Fisher’s Exact Tests were performed between sites to determine statistical significance relative to each order. Amphipod and Isopod compositions differed between site 1 and site 7, producing a R2 value of less than 0.05. However, in Odonata, we did not have a sufficient number of samples to produce any significant results.
Audrey Ragsac
Clinton Cleveland
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Clinton Cleveland
5470 Manila Avenue
Oakland, CA 94618
H 510.601.1755
M 415.577.6329
Nicholas Hu
Clinton Cleveland
Vickie Ly
Vickie Ly