Turbidity As A Control On Phytoplankton Biomass And Productivity In Estuaries Pdf

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Turbidity as a control on phytoplankton biomass and productivity in estuaries

Metrics details. Sundarbans is the single largest deltaic mangrove forest in the world, formed at estuarine phase of the Ganges - Brahmaputra river system. But unfortunately estuarine dynamics of tropical and subtropical estuaries have not yet received proper attention in spite of the fact that they experience considerable anthropogenic interventions and a baseline data is required for any future comparison. Various physical and chemical parameters of water column like pH, temperature, conductivity, dissolved oxygen, turbidity, suspended particulate matter, secchi disc index, tidal fluctuation and tidal current velocity, standing crop and nutrients were measured along with water column productivity.

Relationship of net water column productivity with algal biomass standing crop , nutrient loading and turbidity were determined experimentally. Correlations of bacterial abundance with community respiration and nitrification rates were also explored. Annual integrated phytoplankton production rate of this tidal estuary was estimated to be Gross primary productivity showed marked inter annual variation being lowest in monsoon and highest in postmonsoon period.

Average primary production was a function of nutrient loading and light penetration in the water column. High aquatic turbidity, conductivity and suspended particulate matter were the limiting factors to attenuate light penetration with negative influence on primary production.

Community respiration and nitrification rates of the estuary were influenced by the bacterial abundance. The estuary was phosphorus limited in postmonsoon whereas nitrogen-limited in premonsoon and monsoon period. High algal biomass and primary productivity indicated the estuary to be in eutrophic state in most of the time throughout the year. Our study also indicated a seasonal shifting between autotrophic and heterotrophic conditions in Sundarban estuarine ecosystem and it is a tropical, well mixed high tidal influx and marine dominated no fresh water connection system.

Phytoplankton biomass and primary production mainly depend on nutrient dynamics of coastal and estuarine ecosystems [ 1 , 2 ]. Anthropogenic inputs of excess nutrients to coastal waters is a global problem and has increased dramatically over last few decades [ 1 , 3 , 4 ]. These interventions affect phytoplankton dynamics and primary productions to a great extent [ 5 ].

On the other hand enhanced nutrient loading also stimulates primary production [ 2 , 3 ]. Phytoplankton are known for their rapid responses to altered environmental conditions [ 6 ], such as anthropogenically introduced eutrophication of coastal waters [ 7 ], alteration of coastal configuration, degradation of environmental conditions e. The dynamic structure of phytoplankton communities directly reflects the health of aquatic ecosystems [ 10 ].

In India, Ganges-Brahmaputra estuary is particularly vulnerable to anthropogenic perturbations due to high nutrient loads from riverine discharge, increasing human population density and rapid economic growth [ 11 , 12 ]. In Indian Sundarbans a huge quantity of leaf litter is loaded to the estuarine water from surrounding mangrove forests.

Land mass washes during monsoon and effluents from shrimp culture farms also contribute to this huge nutrient load. Nutrient enrichment or loading has already been identified as a serious problem in recent times in many estuaries [ 13 ] in the world namely Baltic sea, Adriatic sea, Gulf of Maxico, Chesapeake Bay and San Francisco Bay especially during rapid growth of population, agriculture and fertilizer production [ 1 , 2 ].

Rates and patterns of nutrient assimilation vary widely among the coastal ecosystems all over the world. While some estuaries exhibits acute eutrophication leading to enhanced algal biomass and primary production, other nutrient rich estuaries maintain low algal biomass and primary production [ 2 ]. Estuarine dynamics has been well studied in temperate system such as Chesapeake Bay [ 14 , 15 ], San Francisco Bay [ 16 ], and the Baltic sea [ 17 ].

Tropical and subtropical estuaries received comparatively less study but are experiencing noticeable anthropogenic alterations [ 18 , 19 ]. Estuaries are highly dynamic systems linking land to the ocean with large seasonal and spatial gradients of biogeochemical compounds and processes [ 20 ].

They are often greatly influenced by anthropogenic activities, including enhanced organic matter and nutrient loadings. Net ecosystem metabolism NEM , the net effect of production and respiration, in coastal and estuarine environments is a means to evaluate whether such environments are sources or sinks of carbon [ 21 , 22 ]. NEM is positive autotrophic when production exceeds respiration and negative heterotrophic when respiration exceeds production. Most estuaries are net heterotrophic [ 21 , 22 ] and generally a net source of CO 2 to the atmosphere [ 23 — 25 ].

The balance between organic matter and nutrient loading is critical in determining the balance between autotrophy and heterotrophy at the ecosystem level [ 26 , 27 ]. Our study area, Jharkhali estuary is a part of Hoogly-Matla estuary situated in Indian Sundarbans surrounded by the mangrove forests Figure 1. Our study period consists of three seasons namely postmonsoon, premonsoon and monsoon. Present work reports the productivity of this subtropical estuary and explores its correlation with standing crop, nutrient concentration, turbidity, tidal fluctuation and tidal current velocity.

Many other physicochemical parameters like temperature, conductivity, dissolved oxygen concentration DO , sechhi depth were also monitored throughout the study period. Bacterial abundance was also estimated and its relationship with community respiration and nitrification rates was worked out.

In a nutshell, this work explores the estuarine metabolism as a function of both physico-chemical and biological processes. The study area includes Jharkhali Island in the north-central part. Two major channels namely Matla and Bidya run respectively on eastern and western sides of Jharkhali. Apart from this creek, several smaller creeks and rivulets present within the study area also act as conduits of water from both sides.

Both Bidya and Matla rivers are flanked by inhabited islands and mangrove islands. Altogether 11 eleven sample points were selected Table 1 , Figure 1. Out of these eleven points, points 5 and 6 lie in Matla River and Points 1, 2, 3, 4 and 11 are within Bidya River, while points 7, 8, 9 and 10 lie within the Baro Herobhanga Khal creek joining these two mighty rivers. These points have been selected keeping in mind the hydrodynamics of the region.

Samples were collected from the water surface 0. Field trips were arranged at each fortnight and approximately sixty trips were conducted to collect the samples. Collected samples were filtered for the study of physicochemical and biological parameters.

Samples were preserved in cold condition and transported to the laboratory within three hours of collection to analyze immediately.

A suit of environmental variables such as temperature, pH, conductivity, turbidity, light, tidal fluctuation, current speed, nutrients were measured along with primary productivity for three years study period in Sundarban estuary. Dissolved oxygen DO concentration was determined according to Winkler method [ 27 ], nutrients like total nitrogen TN , total phosphate TP , silicate and ammonia were measured according to the standard methodology [ 28 ]. The light attenuation coefficient was evaluated by an empirically derived relationship of 1.

Subsamples for suspended load SPM were filtered through pre-weighed 0. The difference between the two weights equaled the amount of suspended load in the water [ 29 ]. It has high accuracy, piezo-resistive pressure sensors and a fast response PRT temperature sensor as standard. Chlorophyll samples are drawn from all stations, with a maximum vertical spacing of 10 m through the chlorophyll maximum layer; at least one sample is always taken within 5 m of the maximum concentration.

Chlorophyll-a was determined spectrofluorimetrically [ 30 ]. Phytoplankton standing crop biomass was estimated by cell counting method. Total number of phytoplankton present in a litre of water sample was calculated using the following relation:.

Quantitative estimation of bacterial population was performed using Zeiss confocal fluorescence microscope. Bacterial cells were counted on black polycarbonate nucleopore membrane pore size: 0. Primary productivity in a water body can be determined by different methods following the guidance of APHA [ 34 ]. We adopted the oxygen method where changes in oxygen concentration were measured in light and dark bottles.

Planktonic photosynthesis rates were derived in terms of evolved oxygen in the process. These rates were converted into carbon units assuming photosynthetic quotient PQ of 1. One of the sources of uncertainty in estimating gross primary production GPP is the metabolic activity of chemoautotrophic bacteria. This bacterial population is very active in estuaries and consumes significant quantity of oxygen in nitrification process.

The oxygen consumption should be included to avoid overestimation of community respiration CR. Samples were collected at each preselected depth on the basis of light availability in light bottles, dark bottles with and without nitrification inhibitor and in initial analysis bottles, each in triplicates.

Light and dark bottles were suspended at the collection depth and incubated in the middle of the photic zone for 12 hours from 6 AM to 6 PM.

At the end of the incubation period light and dark bottles were similarly fixed and all the bottles were brought back to laboratory in cold condition for analysis. In the dark bottles, amount of oxygen was reduced due to its consumption in respiration of plants, animals and bacteria, known as community respiration CR. But in addition to community respiration, nitrification NH 4 — NO 3 also consumed oxygen from water. Therefore, two metabolic processes i.

But in the dark bottle with nitrification inhibitor NI , only respiration was responsible for oxygen consumption and therefore change in oxygen concentration provided the measure of community respiration CR only. In the dark bottle without nitrification inhibitor both respiration and nitrification were involved in oxygen consumption. So, the difference in oxygen concentration in the dark bottle with and without NI provided nitrification rate.

In the light bottle all the three metabolic processes namely photosynthesis produced oxygen , respiration consumed oxygen and nitrification consumed oxygen occurred simultaneously. The difference in oxygen concentration in the light bottle provides net primary productivity NPP. Samplings were made from eleven stations in triplicate and they were treated as subsamples. Reading of each month represented an average of samples. Temperature of the estuary showed predicted range of variability indicating lowest in postmonsoon in the month of January The pH of water was weakly alkaline and more or less constant throughout the study period 8—8.

The salinity of water increased gradually from postmonsoon Highest salinity was observed in June Moderate to high DO concentration 6. This observation was also reflected in secchi disc indices Nutrient concentration i. TN and ammonia-nitrogen were estimated to be Highest TN and ammonia-nitrogen concentration were observed in the month of February Total phosphate concentration was estimated to be 2. Silicate concentration was observed to be Highest silicate concentration was recorded in October TN:TP ratio was greater than Redfield ratio in postmonsoon averaged Maximum tidal range on Day 07 6.

Subsequent highest peak on Day 22, having average tidal range 5. Tidal fluctuation ranged from 5.

Turbidity as a control on phytoplankton biomass and productivity in estuaries

In recent decades, increasing frequency and intensity of saltwater intrusion in the Modaomen Channel has threatened the freshwater supply in the surrounding cities of the Pearl River Estuary, and ulteriorly changed the environmental conditions of the estuarine waters. Phytoplankton biomass, primary production PP and species composition, as well as hydrological and chemical parameters were examined along a downstream transect in the Modaomen Channel during neap tide NT and spring tide ST , when a strong saltwater intrusion event occurred in late September, A total of 46 species phytoplankton were identified, including Bacillariophyta 25 species , Dinoflagellate 14 species , Chlorophyta 4 species , Cyanophyta 2 species and Euglenozoa 1 species. The dominant species were shifted from freshwater diatoms e. Generally, phytoplankton density, biomass chl- a and PP decreased from the upper to lower reaches along the channel, and were significantly higher in NT than those of ST. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: All relevant data are within the paper and its Supporting Information files.

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Picophytoplankton PicoP are increasingly recognized as significant contributors to primary productivity and phytoplankton biomass in coastal and estuarine systems.


Many estuaries have longitudinal gradients in productivity that mirror the distribution of suspended sediments: productivity is low near the riverine source of sediments (low Zp: Zm) and increases toward the estuary mouth where turbidity decreases.


Turbidity as a control on phytoplankton biomass and productivity in estuaries

These systems, which are characterized by high tidal energy, generally exhibit lower levels of chlorophyll a than systems with lower tidal energy. A comparative analysis of data from 40 microtidal and macrotidal estuaries shows that mean annual chlorophyll a levels are significantly lower in systems with high tidal energy even when nitrogen concentrations are equal to nitrogen levels in the microtidal systems. Tidal range and associated processes e. This is a preview of subscription content, access via your institution.

Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI: Cloern Published Environmental Science. Abstract In many coastal plain estuaries light attenuation by suspended sediments confines the photic zone to a small fraction of the water column, such that light limitation is a major control on phytoplankon production and turnover rate.

Metrics details. Sundarbans is the single largest deltaic mangrove forest in the world, formed at estuarine phase of the Ganges - Brahmaputra river system. But unfortunately estuarine dynamics of tropical and subtropical estuaries have not yet received proper attention in spite of the fact that they experience considerable anthropogenic interventions and a baseline data is required for any future comparison. Various physical and chemical parameters of water column like pH, temperature, conductivity, dissolved oxygen, turbidity, suspended particulate matter, secchi disc index, tidal fluctuation and tidal current velocity, standing crop and nutrients were measured along with water column productivity. Relationship of net water column productivity with algal biomass standing crop , nutrient loading and turbidity were determined experimentally.

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Phytoplankton biomass in estuarine and continental shelf regions are regulated and modified by physical processes, but these interactions have mostly been investigated at a scale of tens of kilometers, and the role of meso- to sub-mesoscale dynamical processes of freshwater plumes in regulating the spatial and temporal variations of algal biomass is largely unknown. Discrete stations were also occupied to allow for the characterization of nutrients. Multiple physical features at different scales regulated the spatial variation of phytoplankton biomass. Phytoplankton biomass was initialized by an improved irradiance field driven by reduced turbidity together with a rapid development of subsurface stratification at the main plume front isohaline of 23 downstream from the turbidity maximum zone. Phytoplankton blooms did not occur until outcrops located within the main front that were characterized by surface convergence and downwelling, which contributed to large algal biomass by mass trapping and enhanced light penetration. Wave-like features were detected seaward of the main front, coinciding with deacceleration of currents, indicating that they are front-released internal waves that increase algal retention time. This study revealed the critical role of small-scale processes near the plume front in triggering phytoplankton blooms under the large-scale context of improved light conditions, coastal upwelling and nutrient additions from intruding oceanic waters.

These systems, which are characterized by high tidal energy, generally exhibit lower levels of chlorophyll a than systems with lower tidal energy. A comparative analysis of data from 40 microtidal and macrotidal estuaries shows that mean annual chlorophyll a levels are significantly lower in systems with high tidal energy even when nitrogen concentrations are equal to nitrogen levels in the microtidal systems. Tidal range and associated processes e. Download to read the full article text. Allen, G.

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In estuaries, the sources of organic matter, its composition, and its functional role in the coastal ecosystem food web are all influenced by dominant estuarine processes. We investigated seasonal variations in the quantity and composition of dissolved inorganic nutrients, suspended particulate matter SPM , and phytoplankton across a low-turbidity estuarine—coastal continuum in Gwangyang Bay, South Korea. The channel carries river discharge, with a large quantity of nutrients NO 3 and SiO 2 , into the bay. The especially low SPM concentrations in the estuary range: 2. Short water-residence times, within the bay system, impede the accumulation of diverse-origin organic matter. The community composition of phytoplankton, distinguished by their size group, also plays a role in characterizing SPM quantity and composition. Estuarine processes play a pivotal role in structuring the seasonal and spatial patterns of biogeochemical cycles in the coastal zone where riverine and marine waters interact Bianchi, ; Cloern et al.

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