Integrated real-time monitoring system to investigate the hypoxia in a shallow wind-driven bay

Corpus Christi Bay (Texas, USA) is a shallow wind-driven bay which experiences hypoxia (dissolved oxygen < 2 mg/L) during the summer. Since this bay is a very dynamic system, the processes that control the hypoxia can last on the order of hours to days. Monitoring systems installed on a single type of platform cannot fully capture these processes at the spatial and temporal scales of interest. Therefore, we have integrated monitoring systems installed on three different platform types: (1) fixed robotic, (2) mobile, and (3) remote. On the fixed robotic platform, an automated profiler system vertically moves a suite of water quality measuring sensors within the water column for continuous measurements. An integrated data acquisition, communication and control system has been configured on our mobile platform (research vessel) for synchronized measurements of hydrodynamic and water quality parameters at greater spatial resolution. In addition, a high-frequency radar system has been installed on remote platforms to generate surface current maps for the bay. With our integrated system, we were able to capture evidence of a hypoxic event in summer 2007; moreover, we detected low dissolved oxygen conditions in a part of the bay with no previously reported history of hypoxia.     

Hydrodynamic characterization of Corpus Christi Bay through modeling and observation

Christi Bay is a relatively flat, shallow, wind-driven system with an average depth of 3–4 m and a mean tidal range of 0.3 m. It is completely mixed most of the time, and as a result, depth-averaged models have, historically, been applied for hydrodynamic characterization supporting regulatory decisions on Texas coastal management. The bay is highly stratified during transitory periods of the summer with low wind conditions. This has important implications on sediment transport, nutrient cycling, and water quality-related issues, including hypoxia which is a key water quality concern for the bay. Detailed hydrodynamic characterization of the bay during the summer months included analysis of simulation results of 2-D hydrodynamic model and high-frequency (HF) in situ observations. The HF radar system resolved surface currents, whereas an acoustic Doppler current profiler (ADCP) measured current at different depths of the water column. The developed model successfully captured water surface elevation variation at the mouth of the bay (i.e., onshore boundary of the Gulf of Mexico) and at times within the bay. However, large discrepancies exist between model-computed depth-averaged water currents and observed surface currents. These discrepancies suggested the presence of a vertical gradient in the current structure which was further substantiated by the observed bi-directional current movement within the water column. In addition, observed vertical density gradients proved that the water column was stratified. Under this condition, the bottom layer became hypoxic due to inadequate mixing with the aerated surface water. Understanding the disparities between observations and model predictions provides critical insights about hydrodynamics and physical processes controlling water quality.     

Status and Trends of Dissolved Oxygen in Corpus Christi Bay, Texas, U.S.A.

The purpose of this studywas to determine status and long-term trends of dissolved oxygen concentrations (DO) in Corpus Christi Bay, Texas, U.S.A. A 20-year record of randomized stations was used to determine the trend of surface water DO, salinity, and temperature over space and time. A 13-year record of two fixed stations was used to determine the temporal nutrient trends. A 10-year record of fixed stations in the southeastern region of Corpus Christi Bay was used to determine the status of disturbance caused by low DO in bottom waters. From 1982 to 2002, there was a significant decrease in surface water DO at a rate of 0.06 mg L⁻¹ yr⁻¹ and a significant increase in surface water temperature at a rate of 0.07°C yr⁻¹. The southeastern region of Corpus Christi Bay had the lowest average DO, and during July and August, DO are steadily declining at a rate of 0.09 mg L⁻¹ yr⁻¹. It is not likely that eutrophication is causing hypoxia, because freshwater inflow rates have significantly decreased since 1941 and nutrient levels have not changed from 1987 to 2000. Even though long-term trends indicate that average surface DO is decreasing, disturbance by hypoxia appears to be stable, but this may be due to just eight years of data. In fact, if the current trend continues, surface water DO will not meet exceptional aquatic life standards (≤5 mgL⁻¹) in 2032.     

The effects of opening an artificial tidal inlet on hydrography and estuarine macrofauna in Corpus Christi, Texas

Packery Channel is part of a complex of storm washover channels which, before 1912, have opened intermittently, linking the Laguna Madre and Corpus Christi Bay, Texas with the Gulf of Mexico. On 21 July 2005, with the assistance of Hurricane Emily, Packery Channel was prematurely opened to the Gulf of Mexico, months before construction of a dredged channel was scheduled to be completed. A before-versus-after, control-versus-impact (BACI) design was used to assess the effects of reopening Packery Channel on water quality and estuarine macrofauna in Mollie Beattie Coastal Habitat Community (MBCHC), Corpus Christi Bay. Two deep (approximately 1 m below m.s.l.) and two shallow (approximately 0.2 m below m.s.l.) stations were sampled monthly for physical and biological characteristics at both control and impact sites between November 2003 and March 2009. The opening of Packery Channel created a unique situation where salinities decreased after the channel opening by ameliorating hypersalinity in Laguna Madre rather than increasing salinities as would occur in most estuaries worldwide. Salinity also fluctuated in a diurnal pattern after the opening of Packery Channel. Apart from salinity, Packery Channel has caused little hydrographic change in MBCHC since opening in July 2005. There was little effect on the macrofaunal community composition. There was a greater difference in community composition between deep and shallow stations than between either before and after or control and impact sites. There have been no significant changes in abundance, biomass, or N1 diversity caused by the opening of Packery Channel.     

Identification of spatiotemporal nutrient patterns in a coastal bay via an integrated k-means clustering and gravity model

This study presents an integrated k-means clustering and gravity model (IKCGM) for investigating the spatiotemporal patterns of nutrient and associated dissolved oxygen levels in Tampa Bay, Florida. By using a k-means clustering analysis to first partition the nutrient data into a user-specified number of subsets, it is possible to discover the spatiotemporal patterns of nutrient distribution in the bay and capture the inherent linkages of hydrodynamic and biogeochemical features. Such patterns may then be combined with a gravity model to link the nutrient source contribution from each coastal watershed to the generated clusters in the bay to aid in the source proportion analysis for environmental management. The clustering analysis was carried out based on 1 year (2008) water quality data composed of 55 sample stations throughout Tampa Bay collected by the Environmental Protection Commission of Hillsborough County. In addition, hydrological and river water quality data of the same year were acquired from the United States Geological Survey's National Water Information System to support the gravity modeling analysis. The results show that the k-means model with 8 clusters is the optimal choice, in which cluster 2 at Lower Tampa Bay had the minimum values of total nitrogen (TN) concentrations, chlorophyll a (Chl-a) concentrations, and ocean color values in every season as well as the minimum concentration of total phosphorus (TP) in three consecutive seasons in 2008. The datasets indicate that Lower Tampa Bay is an area with limited nutrient input throughout the year. Cluster 5, located in Middle Tampa Bay, displayed elevated TN concentrations, ocean color values, and Chl-a concentrations, suggesting that high values of colored dissolved organic matter are linked with some nutrient sources. The data presented by the gravity modeling analysis indicate that the Alafia River Basin is the major contributor of nutrients in terms of both TP and TN values in all seasons. With this new integration, improvements for environmental monitoring and assessment were achieved to advance our understanding of sea-land interactions and nutrient cycling in a critical coastal bay, the Gulf of Mexico.     

Characterization of organic chemical contaminants in sediments from Jobos Bay, Puerto Rico

Jobos Bay, located on the southeastern coast of Puerto Rico, contains a variety of habitats including mangroves, seagrass meadows, and coral reefs. The watershed surrounding the bay includes a number of towns, agricultural areas, and the Jobos Bay National Estuarine Research Reserve (NERR). Jobos Bay and the surrounding watershed are part of a Conservation Effects Assessment Project (CEAP), involving the Jobos Bay NERR, the US Department of Agriculture, and the National Oceanic and Atmospheric Administration (NOAA) to assess the benefits of agricultural best management practices (BMPs) on the terrestrial and marine environments. As part of the Jobos Bay CEAP, NOAA collected sediment samples in May 2008 to characterize over 130 organic chemical contaminants. This paper presents the results of the organic contaminant analysis. The organic contaminants detected in the sediments included polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls, and the pesticide DDT. PAHs at one site in the inner bay near a boat yard were significantly elevated; however, all organic contaminant classes measured were below NOAA sediment quality guidelines that would have indicated that impacts were likely. The results of this work provide an important baseline assessment of the marine environment that will assist in understanding the benefits of implementing BMPs on water quality in Jobos Bay.     

Monitoring the formation of structures and patterns during initial development of an artificial catchment

The objective of this paper is to present observations, results from monitoring measurements, and preliminary conclusions about the development of patterns and structures during the first 5 years of development of an artificial catchment starting from point zero. We discuss the high relevance of initial system traits and external events for the system development and draw conclusions for further research. These investigations as part of a Collaborative Research Center, aim to disentangle and understand the feedback mechanisms and interrelationships of processes and their co-development with spatial and temporal structures and patterns by studying an initial, probably less complex ecosystem. Therefore, intensive measurements were carried out in the catchment with regard to the development of surface structures, hydrological patterns, vegetation dynamics, water chemistry, and element budgets. During the first 5 years, considerable changes within the catchment were observed. Both internal and external factors could be identified as driving forces for the formation of structures and patterns in the artificial catchment. Initial structures formed by the construction process and initial substrate characteristics were decisive for the distribution and flow of water. External factors like episodic events triggered erosion and dissection during this initial phase, promoted by the low vegetation cover, and the unconsolidated sandy substrate. The transformation of the initial geosystem into areas with evolving terrestrial or aquatic characteristics and from a very episodic to a more permanent stream network and discharge, together with the observed vegetation dynamics increased site diversity and heterogeneity with respect to water and nutrient availability and transformation processes compared with the more homogenous conditions at point zero. The processes and feedback mechanisms in the initial development of a new landscape may deviate in rates, intensity, and dominance from those known from mature ecosystems. It is therefore crucial to understand these early phases of ecosystem development and to disentangle the increasingly complex interactions between the evolving terrestrial and aquatic, biotic, and abiotic compartments of the system. Long-term monitoring of initial ecosystems may provide important data and parameters on processes and the crucial role of spatial and temporal structures and patterns to solve these problems. Artificially created catchments could be a suitable tool to study these initial developments at the landscape scale under known, designed, and defined boundary conditions.     

A Three-Dimensional Hydro-Environmental Model of Dublin Bay

In this study, the impact of Escherichia coli emissions from a sewage treatment plant on the bathing water quality of Dublin Bay (Ireland) is assessed using a three-dimensional hydro-environmental model. Before being discharged, the effluent from the plant is mixed with cooling water from a thermal?Celectrical power generation plant, creating a warm buoyant sewage plume that can be 7?C9°C higher and is less saline than the ambient water in the bay. The ability of the three-dimensional model in representing such a stratified condition is assessed based on a comparison of its results with two-dimensional modelling results. Hydrodynamic simulations of water levels and flow velocities in Dublin Bay were obtained using the TELEMAC-3D model in one case and the depth-averaged TELEMAC-2D model in the other. The results of each model were separately used as inputs to the water quality model SUBIEF-3D to simulate the transport and fate of E. coli in the bay and to generate maps of E. coli concentrations over the bay. In addition, the necessity for three-dimensional modelling in simulating the effects of wind direction on the dispersion of E. coli was demonstrated by comparing the results of three-dimensional and two-dimensional model simulations with a number of different wind directions. The comparison showed that the three-dimensional model performed better than the depth-averaged model in simulating the hydrodynamics and resulted in better simulation of the water quality processes in the bay. In particular, the three-dimensional model had reasonably simulated the timing of the delivery of E. coli to the bay. Moreover, the effect of wind on the movement of the buoyant plume of pollution and on the E. coli distribution was found to be more pronounced with the three-dimensional hydrodynamics. The results demonstrate the need for three-dimensional simulations in situations of density differences or significant wind influences.     

Effects of Organic Material and Distribution of Fecal Coliforms in Chetumal Bay, Quintana Roo, México

Most wastewater from the city of Chetumal is discharged into the adjoining bay without treatment through a pluvial sewer system. The bay also receives a high volume of vegetal organic material from the River Río Hondo. The average of biochemical oxygen demand (BOD) was 32.26 mg l-1, it was low compared with other reports and should be indicative of self-depuration processes in Chetumal Bay. In the area most used by the public for recreational and fishing activities, concentrations of fecal coliforms above the limit established by Mexican Legislation were shown. The border between Mexico and Belize is Chetumal Bay, which recently was declared a protected area for manatees.     

Using diatoms as quality indicators for a newly-formed urban lake and its catchment

Periphytic diatoms were studied to evaluate the water quality of a newly created lake, formed by the enclosure of the formerly tidal Cardiff Bay (Wales, UK), and the effects of two inflowing rivers which drain densely populated and industrialised catchments. Seven sites in Cardiff Bay and two locations on the inflowing rivers were monitored for diatoms and water chemistry over 2 years. Water quality was assessed using a revised UK trophic diatom index (TDI) and new methods to determine ecological quality ratios and ecological status classes as required by the EU Water Framework Directive. Diatom assemblages reflected spatiotemporal variations in environmental conditions between the rivers and Cardiff Bay and within the bay. In the bay, diatoms reflected differences in river quality and possibly local pollution in certain areas of the lake. High values of the TDI indicated eutrophic to hypertrophic conditions in both rivers and in the bay and diatoms indicated poor ecological status.     

莱州湾表层沉积物中多氯联苯的测定方法及分布特征探究

以加速溶剂萃取法 (ASE)、索氏提取法/气相色谱法测定了莱州湾表层沉积物中的12种PCBs的浓度水平,探讨了它的分布特征并将两种方法进行了对比;同时测定了渤海湾北部海域表层沉积物中PCBs的含量,与莱州湾进行了比较。结果表明,莱州湾海域表层沉积物检测出8种多氯联苯(PCBs),浓度范围是N.D.~48.40 ng ·g ^-1dw。该海域多氯联苯的分布特征是近岸高,离岸低,由近岸向湾外延伸方向依次递减;渤海湾PCBs的浓度范围是0.15~68.30 ng ·g ^-1dw,和莱州湾差别不大。索氏提取法测定12种多氯联苯类化合物的基质加标回收率为78.00%~104.85%,相对标准偏差为0.95%~3.64%;加速溶剂萃取法的基质加标回收率为90.00%~102.00%,相对标准偏差为0.65%~2.75%;相对于渤海湾北部海域而言,莱州湾区域只是受到轻度污染,属于低风险生态区,不会对生物产生毒副作用;而前者则处于中度污染水平,可能会对生物产生毒副作用。     

Distribution and temporal variation of trace metal enrichment in surface sediments of San Jorge Bay, Chile

Cu, Pb, and Hg concentrations were determined in surface sediment samples collected at three sites in San Jorge Bay, northern Chile. This study aims to evaluate differences in their spatial distribution and temporal variability. The highest metal concentrations were found at the site “Puerto”, where minerals (Cu and Pb) have been loaded for more than 60 years. On the other hand, Hg does not pose a contamination problem in this bay. Cu and Pb concentrations showed significant variations from 1 year to another. These variations seem to be a consequence of the combination of several factors, including changes in the loading and/or storage of minerals in San Jorge Bay, the dredging of bottom sediments (especially at Puerto), and seasonal changes in physical–chemical properties of the water column that modify the exchange of metals at the sediment–water interface. Differences in the contamination factor and geoaccumulation index suggest that pre-industrial concentrations measured in marine sediments of this geographical zone, were better than geological values (average shale, continental crust average) for evaluating the degree of contamination in this coastal system. Based on these last two indexes, San Jorge Bay has a serious problem of Cu and Pb pollution at the three sampling locations. However, only Cu exceeds the national maximum values used to evaluate ecological risk and the health of marine environments. It is suggested that Chilean environmental legislation for marine sediment quality—presently under technical discussion—is not an efficient tool for protecting the marine ecosystem.     

烟台四十里湾赤潮发生与生态环境污染研究

烟台四十里湾海域为赤潮频发区,就赤潮发生的区域分布与其生态环境污染进行探讨研究,以引起社会有关方面正确认识和评价水产养殖业对海洋环境的影响。结果显示: (1)1998~2008年间排入四十里湾的各类污染物总量以贝类养殖排泄物居首,赤潮发生的几率及范围与贝类养殖面积、N、P和C排泄物年际变化有直接必然关系; (2)湾内初级生产力较高,由贝类养殖排泄转化的无机碳占湾内基础物质总量的65%~90％; (3)湾内赤潮生物16种,优势种有红色裸甲藻、中肋骨条藻、海链藻,红色裸甲藻是该湾引起赤潮最常见的赤潮生物种; (4)四十里湾最大流发生在养马岛以外的东北水域,流速值在17~20cm/s 左右,养马岛西南端流速最低,仅为4~5cm/s左右,受水建工程和筏式养殖的干扰,养殖区内流速有所减缓,不利于污染物扩散。研究表明,特定的地理环境及物质条件十分适合藻类的生长繁殖,一旦遇到适宜的水文气象条件,赤潮藻即有骤然快速增殖而形成赤潮。     

Diel Variability of Water Quality in a Tropical Polluted Bay

The objective is to describe and quantify the diel variability of water quality in a tropical coastal system, Guanabara Bay, Brazil. Water samples were collected in spring and neap tide cycles over 24 h periods at three strategic sites. A pollution gradient was evident between the sampling sites. The average fecal coliform values decreased from 10⁶ (site 3, most polluted) to 10¹ (site 1, less polluted). Organic matter mineralization was found in a similar gradient to organic pollution. However, complete nitrification was only found associated to regions where the water quality was better. Variability in this data set was determined mostly by the pollution gradient observed, and by tidal influence as well. The poor water quality indicates that the bay undergoes severe environmental stress. However water renewal promoted by tidal action was an important mechanism in diluting the pollution, improving water quality even in ebb tides and in the inner channels. The significance of micro-scale changes in water quality assessment in Guanabara Bay was confirmed, as well as the importance of these strategic sampling sites, reinforcing the importance of these measurements in monitoring programs.     

One-year monitoring survey of organic compounds (PAHs, PCBs, TBT), heavy metals and biomarkers in blue mussels from the Arcachon Bay, France

Marine mussels Mytilus sp. were transplanted on a monthly basis in cages over one year to oyster farms and harbours in the Arcachon Bay (France) in order to assess the water quality of the bay. Contaminant levels (organotin compounds, trace metals, PCBs and PAHs) were measured in tissues of transplanted mussels and mussels from a reference station, along with physiological parameters of the mussels (condition indexes, lipid content and dry weight). Four biomarkers (AChE: acetylcholinesterase activity, GST: gluthathione S-transferase activity, CAT: catalase activity and TBARS: thiobarbituric acid-reactive substance content) were also monitored. The remote stations monitored (oyster parks) exhibited no accumulation pattern of pollutants. Their respective concentrations therefore constitute a background level of the contamination in the bay ([TBT]= 30 ng Sn g(-1) dw, [SigmaHAPs]= 100 ng g(-1) dw, [SigmaPCBs]= 35 ng g(-1) dw). The elevated chemical contamination of the largest harbour of the bay, the Arcachon harbour, can be interpreted in terms of persistence of organotin compounds ([SigmaOTs]= 1500-2000 ng Sn g(-1) dw) and PAHs ([SigmaHAPs]= 4500-5000 ng g(-1) dw) in sediments and, to a lesser extent, of direct inputs of copper ([Cu]= 20 microg g(-1) dw in harbours versus 7 in oyster parks) and petrogenic PAHs ([methylphenanthrenes]= 1600 ng g(-1) dw in the dockyard versus 170 at the gas stations), related to the use of copper-based antifouling paints and to dockyard activity, respectively. However, the Arcachon Bay presents a low contamination level by PCBs and metals, including harbour stations. Furthermore, higher levels of other PAHs (particularly alkyl PAHs such as methylphenanthrenes/1600 ng g(-1) dw) not included in the 16 PAHs from the EPA priority list (usually studied in biomonitoring programmes/1500 ng g(-1) dw) in the Arcachon harbour underline the need to integrate these compounds in biomonitoring of highly PAH-polluted areas such as harbours in order to avoid misinterpretation of the biological responses observed. Biomarker responses were not able to discriminate the different chemical contamination levels recorded in the Arcachon Bay and rather reflected changes in environmental factors. Furthermore, the strong intraspecies variability of biological responses could be due to genetic differences of mussels from the Arcachon Bay. It is the first time that such an integrated monitoring is performed in the Arcachon Bay, also taking into account seasonal variations of chemical contents and biomarkers levels in mussel tissues.     

Application of the benthic index of biotic integrity to environmental monitoring in Chesapeake Bay

The Chesapeake Bay benthic index of biotic integrity (B-IBI) was developed to assess benthic community health and environmental quality in Chesapeake Bay. The B-IBI provides Chesapeake Bay monitoring programs with a uniform tool with which to characterize bay-wide benthic community condition and assess the health of the Bay. A probability-based design permits unbiased annual estimates of areal degradation within the Chesapeake Bay and its tributaries with quantifiable precision. However, of greatest interest to managers is the identification of problem areas most in need of restoration. Here we apply the B-IBI to benthic data collected in the Bay since 1994 to assess benthic community degradation by Chesapeake Bay Program segment and water depth. We used a new B-IBI classification system that improves the reliability of the estimates of degradation. Estimates were produced for 67 Chesapeake Bay Program segments. Greatest degradation was found in areas that are known to experience hypoxia or show toxic contamination, such as the mesohaline portion of the Potomac River, the Patapsco River, and the Maryland mainstem. Logistic regression models revealed increased probability of degraded benthos with depth for the lower Potomac River, Patapsco River, Nanticoke River, lower York River, and the Maryland mainstem. Our assessment of degradation by segment and water depth provided greater resolution of relative condition than previously available, and helped define the extent of degradation in Chesapeake Bay.     

Characterization of land-based sources of pollution in Jobos Bay,Puerto Rico: status of heavy metal concentration in bed sediment

As part of an assessment of land-based sources of pollution in Jobos Bay, Puerto Rico, sediment samples were collected at 43 sites to characterize concentrations of a suite of pollutants, including metals. Fifteen major and trace metals (Ag, Al, As, Cd, Cr, Cu, Fe, Hg, Mn Ni, Pb, Sb, Se, Sn, and Zn) were measured along with total organic carbon and grain size in surficial sediments. For most metals, maximum concentrations were seen in the eastern bay; however, values were still within concentration ranges found in other estuarine systems. In contrast, silver was higher in the western region. In general, metal distribution in the bay was positively correlated with grain size. Additionally, correlations between Al and other metals suggest natural sources for metals. The data presented here suggest that, although the Jobos Bay watershed contains both urban centers along with industrial and agricultural developments, anthropogenic inputs of metals may be negligible.     

Butyltin compounds and their relation with organic matter in marine sediments from San Vicente Bay—Chile

Tributyltin and its degradation products, mono-and dibutyltin have been determined in sediments collected in some representative sites in San Vicente Bay, Chile. The organic matter contents of sediments and water collected simultaneously from the same sampling sites were also determined. High levels of total organic carbon were found in sediments, especially in those from the northern part of the bay (1.80-8.87%). Good correlations were found between total organic carbon and the oxidizable and refractory carbon fractions. Among the butyltin species determined, TBT presented the highest levels, ranging from 14 to 1,560 ng Sn g(-1) dry weight. Concentration ratios of TBT to DBT ranged between 1.33 and 3.10, showing a high degree of contamination in sediments of this Chilean bay. All data obtained were analysed by the chemometric method of principal components analysis. A strong correlation was found between TBT and DBT concentrations in sediments, the different organic matter contents in sediments and water. In marine organisms only TBT was detected, containing the filterer organism Semele solida higher level than Perumytilus purpuratus and Pyura chilensis (220, 150 and 120 ng Sn g(-1) dry weight, respectively). For the alga Rodoficea iridae the TBT concentration was 60 ng Sn g(-1) dw. Comparatively, these values are higher than those reported for the same kind of marine organisms worldwide. The different samples from San Vicente Bay were found to be contaminated by TBT. This contamination can be attributed to the different anthropogenic activities taking place in the bay.     

钦州湾春季水质营养状况分析与评价

根据2010年4月对钦州湾海域调查结果,分析并评价了该海域春季的营养状况。结果表明,表层海水中DIN和SiO₃-Si都为茅尾海钦江入海口含量较高,PO₄-P为茅尾海西南部沿岸增养殖区含量较高,DIN、PO₄-P和SiO₃-Si水平分布上均表现为湾内含量高于湾外。从营养结构看,与Justic等提出的营养盐化学计量限制标准比较,符合P限制条件,PO₄-P可能成为浮游植物生长的潜在限制因子。根据营养状态指数评价模式和有机污染评价指数计算结果显示,2010年春季钦州湾海域营养水平属于中营养水平,有机污染程度属4级,表明钦州湾表层海水水质已达到中度污染。     

Assessment of chlorophyll-a variations in high- and low-flow seasons in Apalachicola Bay by MODIS 250-m remote sensing

Chlorophyll-a (chl-a) is considered as a primary indicator for water quality and foods for oyster growth in Apalachicola estuarine ecosystem. Assessment of chl-a concentration variation in response to river inflow is important for estuarine environmental research and management. In this study, remote sensing analysis has been conducted to evaluate the effects of river inflow on chlorophyll concentrations in Apalachicola Bay of Florida in the northeast Gulf of Mexico. A remote sensing model for chl-a was improved and applied to map spatial distributions of chl-a by using Moderate Resolution Imaging Spectroradiometer (MODIS) 250-m resolution imageries in high-flow and low-flow seasons in 2001 and 2008. Chl-a values approximately ranged from the minimum 6 μg/l to the maximum 29 μg/l in the study period. Maximum chl-a concentration in high-flow season was almost twice above that in low-flow season. The averaged mean and minimum chl-a level in the high-flow season were approximately 42 and 28 % higher than those in low-flow season, respectively. The remote sensing mapping of chl-a was able to show spatial variations of chl-a in the entire bay under different flow conditions, which indicated its advantage over the traditional field data sampling for monitoring water quality over a large area of estuary. The MODIS 250-m remote sensing regression model presented from this study can be used to support monitoring and assessment of the spatial chl-a distribution in the bay for environmental research and management in Apalachicola Bay.