The Pollution Effects of Nitrate and phosphate on Eutrophication Status in Gomishan international wetland

Nitrate and phosphate can be considered as nutrient limiting of primary production and affecting on eutrophication in surface water. Even momentary increase in the nutrient can stimulate tremendous growth and productivity. Phosphorus limitation dominates in tropical terrestrial (because of effects of soil age) and marine ecosystems (because of effects of sequestration in calcareous sediments) while nitrogen limitation is raised in primary production and eutrophication in many estuarine areas. Although the effects of nutrient loading have been less studied in wetland ecosystems but they can strongly affected, by eutrophication. The coastal wetland of Caspian Sea (Gomishan) due to the expansion of drainage systems, urbanization, wastewater and aquaculture, are exposed was the eutrophication occurrence in coast, and rarely been studied. Furthermore, the residence time and climate change affect the eutrophication patterns in different coastal ecosystems. According to these issues, the necessity of this study was obvious in order to determine role limiting of nitrate and phosphate in Gomishan international wetland. In this paper, the relationship between Chlorophyll concentrations, phosphate, nitrate and turbidity and some environmental factors such as water temp, salinity, pH, have been studied.
Matherials and Gomishan international wetland is located in the north of Iran. The wetland from the west separated by a very narrow sandy strip, from the sea. Therefore, almost all its water is supplied through sea communication channels. Sampling in this study during May to September was done and were in six stations along the Gomishan wetlands that were sensitive to loading nutrient, including: estuarine of Gorganrud River (St2), drainage channel of Gomishan City(St3), overflow channel of Alagol international wetland (St4), input (St6) and output (St5)channels of shrimp site and border area of Magtymguly ( St7). Also, was selected one station of Caspian Sea.
Some physical-environmental factors like salinity, pH, turbidity, water temperature, were measured by multiparameter portable system. In the laboratory, the nutrients were measured by a spectrophotometer (Hach Company). Furthermore, 0.5 L phytoplankton sample water from each station, was filtered by vacuum pump (0.45 µ filter paper) in the laboratory. Finally, the absorption of the extracts was read at the wavelengths of chlorophyll a pigments by a spectrophotometer and calculated using trichromatic method. The Linear regression and Pearson’s correlation between the nutrients and chlorophyll a were determined by SPSS.
Discussion of The physic-chemical parameters are the major factors that control the dynamics and structure of the phytoplankton of aquatic ecosystem. Seasonal variations in these parameters have an important role in the distribution, periodicity and quantitative and qualitative composition of the species that live within them. According to the results of physico-chemical parameters in this study, non algal turbidity was high in the Gorganroud estuarine (S2) and the border area of Magtymguly (S7), in addition to Caspian Sea (S1) (Fig 1and2 a). So by reducing it during the study period, the availability rate of orthophosphate was increased (Fig 1and2 c). Non algal turbidity can produce low algal chlorophyll-to-nutrient ratios and cause a lack of relationship between chlorophyll and phosphorus in some regions. Effluent of industrial parks and human wastewater was the main reasons of high turbidity in S2.
Furthermore, in stations mentioned above, in September compared to August, between increasing the concentration of Chla and nitrate and decreasing in orthophosphate, there was a positive correlation. Because nitrogen availability may boost the non-nitrogen-fixing cyanobacterial, and as result nitrogen played the limiting role. S2 and S7 respectively, were the southernmost and northernmost stations in Gomishan wetland.
Changes of hydrological parameters during the study period at some stations
In other studied stations, including drainage channel of Gomishan (S3), overflow channel of Alagol (S4) and input (S5) and output (S6) of shrimp site, between the increase of turbidity, Chla and orthophosphate there was a positive relationship. As a result, phosphorus played the limiting role in these stations. Furthermore, in S3 and S4, that were central stations of wetland, in September compared to August, nitrate concentration was low and orthophosphate was high (Fig 3 and 4 d,c). This issue showed, in the nitrogen resource constraints, as soon as obtaining a small amount of phosphate resources, N/P decreased, and blooms of cyanobacteria level increased in September (Fig 3 and 4 b).
Significant increase of nutrients especially phosphate, indicated the development process of urbanization and wastewater, non-normative increase of aquaculture and farming activities that was effective on hydrologic drought of wetland. Furthermore, the results of Pearson correlation and Linear regression showed the significant correlation of orthophosphate with log Chla (PWe conclude that algal density changes resulting in algal blooms, which are cause wetland water quality degradation may be predicted based on timely sampling and analysis of key water quality parameters especially phosphate. Also for controlling runoff, prevent of development the open drainage channels is essential which abundantly have been seen around the wetland.
Furthermore, interpretation of observed chla concentration, not limited to the inputs and or sediment composition in local scale, because the climate changes also were effective.