Human impact on the silica cycle : reduction of dissolved silica inputs into the ocean as a result of the increasing impervious cover

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Socratis Loucaides (Creator)
Institution
The University of North Carolina Wilmington (UNCW )
Web Site: http://library.uncw.edu/

Abstract: Frequent harmful algal blooms in coastal waters have been linked to increasing nitrogen (N) and phosphorous (P) loadings. Recent studies, however, have shown that dissolved silica (DSi) depletion in natural waters can be an important if not the most important factor that triggers these events. Long term hydrologic and water quality data give signs of significant human impact on the silicon cycle. More specifically, by altering the hydrology of the land, humans may have reduced the amount of DSi that reaches the oceans through freshwater streams. This study examined the hypothesis that a watershed with more impervious cover discharges less DSi per unit watershed than a more undisturbed watershed. DSi discharge data were collected from 2 different freshwater streams with watersheds of different % impervious cover during 5 non-rain and 4 rain events. The stream with higher impervious cover discharged higher DSi per unit watershed during non-rain events. During intense rain events the more impervious watershed rapidly released stormwater as low-DSi runoff while the less impervious watershed released less runoff and more DSi per unit watershed. During low intensity rain events the less impervious watershed released no runoff while DSi discharge increased. The more impervious watershed released runoff even during the lightest event. Using the CN method developed by the Soil Conservation Service, it was found that a more impervious watershed not only produced more runoff than a less impervious watershed, but it also produced runoff more often. Higher volume of runoff can cause short term DSi dilution during rain events as well as long-term reduction of DSi inputs to coastal waters. According to the CN method a long-term reduction of DSi loads is taking place in response to increasing impervious cover. Since diatom primary production is possibly the most important link of the marine food chain, and since diatom growth is DSi limited, reduction of the coastal oceans’ silica budget may have negative impacts on all levels of the food chain.

Additional Information

Publication
Thesis
A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment Of the Requirements for the Degree of Master of Science
Language: English
Date: 2009
Keywords
Algal blooms--North Carolina--Bradley Creek, Marine sediments--Effect of human beings on, Silica, Silicate minerals--North Carolina--Bradley Creek
Subjects
Marine sediments -- Effect of human beings on
Silicate minerals -- North Carolina -- Bradley Creek
Silica
Algal blooms -- North Carolina -- Bradley Creek