Groundwater and Nutrient Discharge into Jiaozhou Bay,North China

The health of near shore marine ecosystems has long been a concern because of its importance to coastal areas. Jiaozhou Bay (JZB) is one such marine ecosystem experiencing rapid water quality degradation in the last several decades. From the area surrounding the bay, the nutrients discharged into the bay through surface water and groundwater has been greatly changed. The thickness of the aquifers and the permeability is relatively high, the concentrations of nutrients in the groundwater are generally high, and so the groundwater discharged into JZB is very significant. However, no attempt has ever been made to evaluate the amount of nutrients discharged into the bay area via groundwater. In this study, the cross-section method and water balance method were used to estimate the amount of groundwater and nutrients discharged into JZB via the subsurface. Groundwater was monitored and sampled at aquifers surrounding the bay area, and some previously available data was also analyzed. The results indicated that groundwater from the Baisha Aquifer east of JZB now is the major source of nutrients (nitrate, dissolved SiO₂) being discharged into the bay. The concentrations of nutrients in the groundwater have been increasing with intensive agricultural land use. However, Dagu Aquifer, the largest aquifer north of JZB, only provides limited nutrients to the bay area because of the construction of a low permeability subsurface dam. Historically, during the 1970s to the 1990s, the Baisha Aquifer experienced seawater intrusion due to excessive groundwater withdrawal. The same was true for the Dagu Aquifer from the 1980s to the 1990s. Because of this, no significant nutrients were discharged into the bay.     

Seasonal Variation of Inorganic Nutrient Uptake by Heterotrophic Bacterioplankton in Jiaozhou Bay,North China

The distribution patterns and factors affecting uptake rates and turnover times of dissolved inorganic nutrients by heterotrophic bacterioplankton (HB) in Jiaozhou Bay were studied based on in situ surveys and laboratory culturing. The uptake rates of dissolved inorganic phosphorus (DIP) and dissolved inorganic nitrogen (DIN) by HB are limited by the temperature of the water and the concentration of dissolved organic carbon. The turnover times of DIP and DIN by HB are regulated by the concentrations of the nutrients and the numbers of HB, which show significant spatiotemporal variability in Jiaozhou Bay. HB may aggravate the P-limitation of phytoplankton by competing for phosphorus in summer in Jiaozhou Bay. HB play an important role in the biogeochemical cycling of nutrients and may increase the N:P ratio and the accumulation of DIN, thereby accelerating the imbalance of the N:P ratio in Jiaozhou Bay.     

Nutrients Seasonal Variation and Budget in Jiaozhou Bay,China: A 3-Dimensional Physical–Biological Coupled Model Study

A 3-D biological model was developed and coupled to a hydrodynamic model, i.e., Princeton Ocean Model, to simulate the seasonal variation and budget of dissolved inorganic nitrogen, phosphate, and silicate in Jiaozhou Bay. The modeled nutrients distribution pattern is consistent with observation. Silicate, the most important limiting element for phytoplankton growth, is characterized by consumption in spring, increase in summer and autumn, and accumulation in winter, whereas dissolved inorganic nitrogen and phosphorous have increasing trend with low rates in spring, due to excessive river loads. Phytoplankton plays an important role in nutrient renewal by photosynthesis and respiration processes. During an annual cycle, 7.83 × 10³ t N, 0.28 × 10³ t P, and 3.93 × 10³ t Si are transported to the bay’s outer sea, i.e., the Yellow Sea, suggesting that Jiaozhou Bay is a significant source of nutrients for the Yellow Sea. The spatial distribution of nutrients is characterized by vertically homogeneous profiles, with high concentration inside the bay and low concentration toward the bay channel. These features are mainly governed by strong turbulent mixing, fluvial influx, water exchange rate, and Yellow Sea water intrusion. Numerical experiments suggest that the government should pay enough attention to proper layout of sewage drainage.     

Speciation and Seasonal Variations of Dissolved Inorganic Arsenic in Jiaozhou Bay,North China

The distributions and biogeochemical cycles of arsenic in the aquatic environment have captured the interest of geochemists due to arsenic’s multiple chemical forms, the toxicity of certain arsenic species and large anthropogenic input. Seasonal variations in the dissolved inorganic arsenic concentration and speciation in Jiaozhou Bay, which is located on the west coast of the Yellow Sea in northern China, are presented here. Three cruises were carried out in Jiaozhou Bay under varying tidal regimes, one at neap tide and one at spring tide in August and one at spring tide in October of 2001. In addition to the transect surveys, the main sources of dissolved inorganic arsenate and arsenite in Jiaozhou Bay, including riverine input from five major tributary rivers, atmospheric dry and wet depositions, and groundwater and wastewater input, were collected in different seasons to estimate arsenic transport through different sources. The mean concentrations of total dissolved inorganic arsenic (TDIAs, As (V+III)) in Jiaozhou Bay were statistically comparable between summer and autumn, with higher concentrations at the northwest and northeast parts of the bay, reflecting human activities. The As (III)/TDIAs ratio ranged between 0.045 and 0.68, with an average of 0.16, implying that arsenate was the dominating species in Jiaozhou Bay. A preliminary box model was established to estimate the water-mass balance and arsenic budgets for Jiaozhou Bay, which demonstrated that river inputs and atmospheric depositions were the main sources of arsenic into Jiaozhou Bay. The concentrations of dissolved inorganic arsenic in Jiaozhou Bay have decreased in the last two decades. Compared with other areas in the world, the concentration of arsenic in Jiaozhou Bay remains at the natural level and this region can be characterized as a less disturbed area.     

Distributions,Land-source Input and Atmospheric Fluxes of Methane in Jiaozhou Bay

CH₄ concentrations in both the surface and bottom waters of Jiaozhou Bay were determined during four surveys in 2003, which showed variability with both seasons and tidal cycles. Atmospheric fluxes of CH₄ in Jiaozhou Bay showed obvious seasonal and spatial variations, with the highest values occurring in summer and the lowest in winter. The annual emission of CH₄ from Jiaozhou Bay was estimated to be . CH₄ in the water column of Jiaozhou Bay was found to come from several land-sources including riverine water input, sewage water input and groundwater input. The spatial and temporal variation in distributions and atmospheric fluxes of CH₄ in Jiaozhou Bay was influenced mainly by the input of polluted river waters and the sewage effluents along the eastern coast, which highlights the effects of human impacts on CH₄ emission rates.     

Watersheds Nutrient Loss and Eutrophication of the Marine Recipients: A Case Study of the Jiaozhou Bay,China

Industrialization and urbanization along the coastal population centers have brought great changes in the land cover and material fluxes from watersheds to receiving bays and estuaries. We have embarked a multiyear research project on “Watersheds Nutrient Loss and Eutrophication of Jiaozhou Bay” for the period of 2000 to 2004, funded by the Natural Science Foundation of China to examine human influence on the marine sector of ecosystem. Jiaozhou Bay, located in the southern part of Shandong Peninsula, was selected because of the existence of long-term hydrographic and meteorological records since the 1930s and recent observations on the marine ecological variables. We have made extensive and periodic measurements on the water movement, nutrients, phytoplankton, and microbe in water column and bottom sediments. Box and 3-dimensional hydrodynamic models were developed and utilized to understand the evolution of eutrophic status with time. It was found that primary productivity has suffered from silica depletion followed by phosphate, and the dominance of large phytoplankton has been replaced by small-size communities. These ecosystem changes were brought by the changes in the relative contribution among major pathways and concentrations, owing to the human activities in the watershed. Eight articles in this volume reported various aspects of the linkage between watershed human activities and ecosystem for the Jiaozhou Bay as the initial outcome of this project.