Hydrobiological Variables Research Articles

Effects of Extreme Climatic Events on the Hydrological Parameters of the Estuarine Waters of the Amazon Coast

Oscillations in rainfall levels are one of the principal factors that determine seasonal shifts in physicochemical and hydrobiological variables, and exceptional climate events can have an enormous effect on the characteristics of small tropical estuaries. Given this, the present study investigated the responses of the physiochemical and hydrobiological variables of a small, shallow, and well-mixed Amazonian estuary with absence of any direct fluvial discharge to different climatic scenarios (typical conditions, and drier events). The study was based on 21 field campaigns conducted between April 2012 and April 2017. During rainy seasons of typical condition, when rainfall levels were higher and salinity lower than 7 (just after a weak La Niña), phytoplankton biomass was affected by increased turbidity (> 400 NTU) of the water, even when nitrogenous compounds were readily available (ammonium: 3.39 ± 1.71 µmol L−1, nitrite 0.90 ± 0.80 µmol L−1, and nitrate (3.91 ± 1.86 µmol L−1). In addition, the absence of any direct fluvial discharge appearance has contributed to the cumulation of phytoplankton biomass (chlorophyll-a > 20 mg m−3) into the estuary during the rainy season of the drier events and typical conditions, when turbidity was lower (< 200 NTU). Conversely, during the dry seasons of the drier events, when rainfall levels were lower, and extremes of salinity were recorded (> 38), phytoplankton biomass (chlorophyll-a < 10 mg m−3) was affected by the lower levels of nitrogenous compounds, even when phosphorous compounds were largely available. Overall, the present study has shown that extreme oscillations in rainfall levels cause abrupt shifts in the physicochemical parameters of the estuary, and affected the phytoplankton biomass, although high turbidity appeared to limit the buildup of this biomass. These effects are manifested immediately in the study area, given that the Taperaçu is a small estuary with a limited freshwater input, and it would seem reasonable to expect similar processes in other minor Amazonian estuaries when subjected to extreme fluctuations in rainfall levels.

Interannual variability in the trophic status and water quality of Bahía Magdalena, Mexico, during the 2015–2018 period: TRIX

The Trophic Index (TRIX) was computed monthly, from January 2015 to December 2018, for ten sites in Bahia Magdalena, Baja California Sur. Hydrobiological variables showed interannual and seasonal variations in the shallow and deep zones of the lagoon. The chlorophyll-a (Chla) was the variable with fewest significant correlations (P < 0.05) during the study period. A significant decrease in TRIX was observed in 2015, compared to all other years, likely related to the effects of warming events such as “El Niño” and “The Blob” (defined as a large mass of relatively warm water in the Pacific Ocean off the coast of North America) in the region. TRIX values in the winter–spring (January to June) were generally higher than those in summer-autumn (July–December) due to the prevailing NW winds that cause coastal upwelling and shallow water mixing, making nutrients available in the lagoon. There was a marked stratification of the water column in the second half of the year that made the surface layer nutrient-poor. We found a high and significant correlation (r=0.66, P < 0.05) between TRIX values and water relative density in the deep zone of the lagoon, denoting the effect of subsurface oceanic water on nutrient concentrations. At the local scale, TRIX values in the shallow zone were generally lower than in the deep zone, but these differences reached statistical significance only in 2018. The monthly average TRIX (5.9 ± 0.2) denotes a high trophic level and mediocre water quality. Although TRIX values might have some shortcomings, these results can be used as an early warning for the relevant stakeholders and authorities.

Energía calórica, biomasa y estructura de los macroinvertebrados acuáticos en la reserva La Nitrera, Concordia, Antioquia, Colombia

El embalse La Nitrera se encuentra localizado a 2140 m.s.n.m. en el municipio de Concordia, departamento de Antioquia (Colombia) y es la única fuente de abastecimiento de agua del municipio. La operación de un embalse sobre un sistema lótico afecta la estructura y ensamblaje de sus ecosistemas acuáticos. Esta investigación tuvo como propósito analizar la distribución de la biomasa de los macroinvertebrados acuáticos antes y después del embalse, con el fin de determinar el impacto de este sobre las comunidades hidrobiológicas. Para tal fin, se analizaron las variables hidrobiológicas en época seca, de lluvia y en diferentes periodos de transición entre el año 2016 y 2017. Se investigaron cuatro estaciones de monitoreo, realizando la determinación, conteo y definiendo el rol trófico de los macroinvertebrados acuáticos, además de un análisis termogravimétrico (TGA) de la biomasa. Con la información obtenida, se construyó un modelo trófico y se calculó la pérdida de energía calórica disponible de la biomasa (TGA). Los resultados evidenciaron que las comunidades de macroinvertebrados acuáticos presentan una modularidad similar entre ellas en las estaciones antes del embalse, y una modularidad diferente en la estación después del embalse. A través del índice de modularidad (modelo Ghepi) y el análisis TGA, se logró establecer que el embalse altera la cadena trófica de las comunidades de macroinvertebrados acuáticos.

Hydrobiological variables as a regulatory factor on the abundance of heterotrophic flagellates in an urban pond

The seasonal abundance of flagellates has been monitored over a period of 1 year from December 2013 to November 2014 (divided into 4 conjugative seasons namely winter, spring, summer, and autumn) in an experimental pond located in Rajshahi City Corporation area, Bangladesh. To our knowledge, this study is the first to shed light on the occurrence and possible interrelationships among heterotrophic flagellates (HF), bacteria and zooplankton in Bangladesh and the result obtained by this study will be beneficial for similar water ecosystem all over the world. Standard methods were used to determine the prescribed hydrological parameters and zooplankton cell density. Maximum HF abundance (14 346.00 cells/mL) was found in the spring and the minimum (5 215.00 cells/mL) occurred in the summer. Inverse to HF, significantly (P<0.05) higher zooplankton abundance was found during the winter (782.00±47.62 cells/mL) and the lowest value was found in the autumn (448.00±39.15 cells/mL). Whereas similar to the HF, total bacterial abundance was significantly higher during the spring ((2.25±1.05)×105 cells/mL) and lower in the summer ((0.79±0.06)×105 cells/mL). Multivariate analyses (ANOSIM and MDS) have shown significant seasonal differences for cell numbers where MDS ordination plot and cluster analysis based on similarity in the genera abundance of HF revealed overlapping condition between winter and spring. Canonical correspondence analysis (CCA) also showed a distinct separation among the genera based on the prevailing hydrological situation and indicated that temperature, pH, BOD5, and NO 3 − were the most important environmental variables in determining the observed variation in HF community structure. Among the biological factors, zooplankton showed negative but total bacteria were positively correlated with HF abundance.

Environmental conditions and primary production in a Sahelian shallow lake (Lake Guiers, North Senegal)

This is a study of the environmental conditions and primary phytoplankton production in a Sahelian shallow lake of Senegal, West Africa. Environmental descriptors (nutrient, water transparency, temperature and hydrochemistry) and their effects on primary production were studied. Samples were collected monthly from March 2002 to February 2003 in 3 stations of the central part of water body. Climatic variables show a marked annual pattern following two dominant wind directions: NNE (North-North-East) and NNW (North- North-West). This cyclic evolution affects hydrobiological variables. In this central part of the lake, water body was not stratified with same measures between surface and bottom. Lake water was turbid with lower values during the maritime trade winds period characterized by high water temperatures and conductivity. Water pH was relatively higher than seven (07) associated with high contents of oxygen (approximately 90%) in all stations. The station Typha is marked by a low pH and high fluctuations in the rates of oxygen (20 to 120%). Nutrient concentrations were low, with high variability (from 0 to 30 μg.l-1 for DIN and from 0 to 18 μg.l-1 for PO4). The primary production in Guiers Lake was high; it showed a vertical gradient with production of 2400 mgC.m-3.days-1 in surface and a low of 200 mgC.m-3 days-1 at the bottom. In this shallow system, environmental conditions regulate the primary production.Keywords: Environmental descriptors, primary production, shallow lake, Senegal.

MODELS OF LAKE LADOGA BASED ON THREE-DIMENSIONAL CELLULAR AUTOMATA

A new approach for modeling complicated nonlinear processes, including processes of self-organization, using so-called cellular automata is suggested. A computer model of the distribution of persistent impurities, assessment of pollution and thermal regime of Lake Ladoga was built as an example. Modeling problems are solved successively from simple to more complex ones: from a zero-dimensional vertical model of the lake’s deep-water area to a two-dimensional model for the lake’s longitudinal section and, finally, three-dimensional model of the entire water body. The generated models are designed so that they can be further expanded to include hydrochemical and hydrobiological variables for simulating lake ecosystems.

Distribution and feeding habitat characterization of whale sharks Rhincodon typus in a protected area in the north Caribbean Sea.

The relationship between the distribution of the whale shark Rhincodon typus and hydrobiological variables in the Caribbean Sea during 2005-2009 was analysed. Monthly trips were made to the R. typus aggregation area during the months when this species is present in the region (May to September) to record sightings and hydrological data and to collect samples to determine nutrients, chlorophyll a (Chl a) and zooplankton biomass. A total of 2104 R. typus were counted and three zones of high abundance were identified: Cabo-Catoche, Contoy (both within the Whale Shark Biosphere Reserve, WSBR) and the zone knows as Afuera. The zones of greatest R. typus density within the WSBR were characterized by high Chl a concentrations (median: 1·1 mg m-3 , interpercentile range: 0·5-1·8 mg m-3 ) and high nutrient concentrations, such as ammonium (median: 2·5 µmol l-1 , interpercentile range: 0·5-6·4 µmol l-1 ), due to the influence of local upwelling. A generalized additive model (GAM) was used to explore the relationship between R. typus distribution and the environmental variables inside WSBR. Zooplankton biomass was the most influential environmental variable, supporting the close relationship between R. typus distribution and biological productivity. Copepods were the dominant zooplankton group within the WSBR. In the Afuera zone, there were large R. typus aggregations (>80 individuals) associated with zooplankton dominated by fish eggs and significantly higher mean ± s.d. biomass (3356·1 ± 1960·8 mg m-3 ) compared with that recorded inside the WSBR (103·5 ± 57·2 mg m-3 ). The differences among zones generated changes in R. typus distribution patterns and provided opportunities to develop local management strategies for this species.

Spatial and temporal dynamics of biotic and abiotic features of temperate coastal ecosystems as revealed by a combination of ecological indicators

Coastal ecosystems exhibit complex spatio-temporal patterns due to their position at the interface between land and sea. This is particularly the case of temperate ecosystems where exploitation of coastal resources (fisheries and aquaculture) and intensive agricultural use of watersheds further complicate our understanding of their dynamics. The aim of the present study was to unravel the spatio-temporal dynamics of contrasted megatidal coastal ecosystems located at the same regional scale (i.e. under the same regional climate), but under different kinds of human pressure. Two kinds of ecological indicators were assessed over a period of four years at 11 locations along the coast of the Cotentin peninsula (Normandy, France). A first set of hydrobiological variables (dissolved nutrients, Chl a, temperature, salinity, etc.) was measured fortnightly in the water column. These data were analysed by principal components analysis (PCA). A second set of variables were the carbon and nitrogen stable isotope ratios of the adductor muscles of cultured Crassostrea gigas introduced every year to typify the bentho-pelagic coupling at each location. Food sources were also investigated using a mixing model with data on the isotopic composition of the food sources obtained previously. To identify which environmental variables played a significant role in determining the oyster diet, the contributions of oyster food sources were combined with environmental variables in a canonical correspondence analysis (CCA). Isotopic values of adductor muscles varied significantly between −20.12‰ and −16.79‰ for δ13C and between 8.28‰ and 11.87‰ for δ15N. The PCA distinguished two groups of coastal ecosystems that differed in their coastal hydrology, nutrient inputs, and the size of their respective watershed, irrespective of the year. In each zone, different spatial patterns in the measured variables were observed depending on the year showing that local impacts differed temporally. As revealed by CCA, food sources used by the oysters were mainly explained by salinity suggesting regional differences between ecosystems. On the west coast of the peninsula, climatic factors act in synergy with anthropogenic factors (i.e. nutrient enrichment) whereas on the east coast, climatic factors appear to be dampened by anthropogenic factors.

Response of macroinvertebrates and water quality to long-term decrease in organic pollution in some Estonian streams during 1990-1998

A survey was started in 1990 of the benthic macroinvertebrate community and water quality in some Estonian streams affected by organic pollution, especially the spreading of slurry on fields. The study was expanded during 1991–1998 to involve 47 sampling sites. Long-term dependence was tested using the SAS/GLM contrast statement. All biological indices used (BMWP-ASPT, number of ASPT scoring families (NASPT), Danish Fauna Index, Belgian Biotic Index, EPT-index) were significantly related to the degree of organic pollution. Compared with the reference sites, the test sites revealed significantly lower water quality: higher BOD7, total P and NH4; lower pH and all hydrobiological indices. Season and stream size at the sampling site (expressed in km from the stream source) had significant effects on both hydrochemical and hydrobiological variables. On the contrary, discharge and precipitation had no significant influence on the studied water quality indicators, with the exception of pH in a few cases. At the same time, all but three variables for the reference and the test sites were different at the beginning of the sampling period; this difference remained only for a few sensitive indices such as ASPT and Danish Fauna Index at the end of the period, indicating general improvement in the environment.

Need for restricting bivalve culture in the southern basin of the Lagoon of Venice

At present, one of the environmental emergencies in the Lagoon of Venice is the impact of short-necked clam (Tapes philippinarum) fishery, which is practically an unregulated fishery. Although one of the proposed solutions would be the restriction of Tapes fishery to licensed areas, high seeding density can cause undesired effects on the environment. In this study several hydrobiological variables are compared between small areas of the Lagoon of Venice traditionally used for bivalve culture (clam, T. philippinarum and mussel, Mytilus galloprovincialis), and areas in the southern basin with seagrass meadows. Labile and suspended organic matter in the water was higher in areas with bivalve farming than in Zostera areas (undisturbed control). The same pattern was recorded for contents of total organic matter and acid volatile sulphides. The biomass of microplankton in farming areas was quite high (0.8–2.7 g m−3). Mesozooplankton was extremely abundant, particularly at night, when its biomass was 1–2 orders of magnitude higher than during the day. Its composition was different in the culture areas and in Zostera areas. The biomass of Tapes in culture beds and their filtering capacity were also estimated.

Hydrobiological consequences of the addition of phosphate precipitants to inlet water of lakes

In three model reservoirs (LUND, 1975) a method reducing bluegreen algal blooms in lakes was studied. Iron or aluminium were added to inlet waters for chemically binding the inflowing phosphorus. The research program, started in 1975, includes intensive monitoring of many chemical and hydrobiological variables, the determination of water and mass balances and since 1977 measurements or primary production rates with14C. In this paper only the results found in 1977 are discussed. An attempt is made to describe quantitatively how growth rates and changes in biomass are interconnected and how phosphorus precipitation changes these variables. In all reservoirs a large discrepancy was observed between the actual rate of increase in the algal population and the relative production rate. The latter appeared to be higher by one order of magnitude. The relative death rate due to grazing can account for the large difference between these growth rates only when selective grazing of zooplankton on phytoplankton is assumed. It can be concluded that treatment of inlet water with AVR, an aluminium salt, is unsuccessful in reducing algal development. Treatment with ironsulphate may be successful, but a reduction of the relative growth rates was not observed. The effects of grazing of zooplankton andDreissena polymorpha need further investigation.

Indicateurs liés à la qualité de l'eau et comportements ; application aux lacs d'Annecy et du Bourget

The investigation of environment indicators is a descriptive approach but it has the advantage of leading fairly rapidly to practical conclusions. We present the results of an application to two Alpine lakes - Annecy and Le Bourget. It is based on a comparison of hydrobiological parameters and socio-economic data. The comparative study of the two lakes leads to a global view in which the purity of the water is of great importance. We demonstrate that it is possible to judge it according to two hydrobiological variables - the colour and turbidness of the water. To go further than this one must distinguish between the various functions of the water. There may be incompatibilities between them which poses the problem of spacial distribution and hence of planning. In practical terms we have built four particular functions (sport, ecology, its ludico-social function and its visual function). For each we propose particular indicators.