Mapping and Assessing Commercial Fisheries Services in the Lithuanian Part of the Curonian Lagoon

The spatial distribution of biomass of main commercial fish species was mapped to estimate the supply of a provisioning fishery service in the Curonian lagoon. Catch per unit effort (CPUE) was used as a proxy to estimate the efficiency of commercial fishing and, subsequently, the potential biomass of fishes. The relationship between distinctive characteristics of the fishing areas and corresponding commercial catches and CPUE was analyzed using multivariate analysis. The total catch values and CPUE used in the analyses were derived from the official commercial fishery records. RDE analysis was used to assess the variation of both catch and CPUE of commercial fish species, while the percentages of bottom sediment type coverage, average depth, annual salinity, and water residence time in each of the fishing squares were used as explanatory variables. This distance e-based redundancy analysis allowed for the use of non-Euclidean dissimilarity indices. Fisheries data spatial distribution map indicated the lack of coherence between the spatial patterns of commercial catches and CPUE distribution in the northern part of the lagoon. Highest CPUE values were estimated in the central-eastern part of the lagoon as compared to the western part of the lagoon where CPUE values were substantially lower. Both total catch and CPUE appeared not to be related to the type of bottom habitats statistically while being spatially correlated in-between. However, the impact of salinity and water residence time calculated using the 3D hydraulic circulation model on the distribution of both CPUE and commercial catches was statistically significant.

Effects of Groundwater Inputs to the Hydraulic Circulation, Water Residence Time, and Salinity in a Moroccan Atlantic Lagoon

The finite element model SHYFEM was used to study the hydrodynamics and variability of water level, salinity, temperature, and water residence time (WRT) in the Oualidia lagoon located on the Moroccan Atlantic coast. The lagoon hosts a RAMSAR convention-protected area and also offers a set of valuable ecosystem services providing the source of income for the local population. To assess the effects of submarine groundwater discharge (SGD) inputs in the study area, four simulations were set up using different SGD inputs estimates in addition to tidal forcing, bathymetry, meteorological data including solar radiation, rain, and wind, in addition to boundary conditions in the Atlantic such as salinity, water level, and water temperature. The model was calibrated and validated using hydrodynamic measurements of previous studies in 2012 and 2013. The final results from the model are in good agreement with measured data. The simulation with SGD input ~0.05 m3 s−1 produced salinity values closest to the observed ones. Calculated spatial distribution of WRT, temperature, and salinity reduced to coordinates in two PCA axes is consistent with lagoon zones developed earlier using the benthic macroinvertebrate distribution. The calculated spatial distribution of WRT allowed us to evaluate the placement of oyster aquaculture farms and small-scale fisheries in relation to water quality issues existing in the lagoon.

A modern snapshot of the isotopic composition of lacustrine biogenic carbonates – Records of seasonal water temperature variability

Carbonate shells and encrustations from lacustrine organisms provide proxy records of past environmental and climatic changes. The carbon isotopic composition (δ13C) of such carbonates depends on the δ13C of dissolved inorganic carbon (DIC). Their oxygen isotopic composition (δ18O) is controlled by the δ18O of the lake water and on water temperature during carbonate precipitation. Lake water δ18O, in turn, reflects the δ18O of precipitation in the catchment, water residence time and mixing, and evaporation. A paleoclimate interpretation of carbonate isotope records requires a site-specific calibration based on an understanding of these local conditions. For this study, samples of different carbonate components and water were collected in the littoral zone of Lake Locknesjön, central Sweden (62.99° N, 14.85° E, 328 m a.s.l.) along a water depth gradient from 1 to 8 m. Samples from living organisms and sub-recent samples in surface sediments were taken from the calcifying alga Chara hispida, mollusks from the genus Pisidium, and adult and juvenile instars of two ostracod species, Candona candida and Candona neglecta. Neither the isotopic composition of carbonates nor the δ18O of water vary significantly with water depth, indicating a well-mixed epilimnion. The mean δ13C of Chara hispida encrustations is 4 ‰ higher than the other carbonates. This is due to fractionation related to photosynthesis, which preferentially incorporates 12C in the organic matter and increases the δ13C of the encrustations. A small effect of photosynthetic 13C enrichment in DIC is seen in contemporaneously formed valves of juvenile ostracods. The largest differences in the mean carbonate δ18O between species are caused by vital offsets, i.e. the species-specific deviations from the δ18O of inorganic carbonate which would have been precipitated in isotopic equilibrium with the water. After subtraction of these offsets, the remaining differences in the mean carbonate δ18O between species can mainly be attributed to seasonal water temperature changes. The lowest δ18O values are observed in Chara hispida encrustations, which form during the summer months when photosynthesis is most intense. Adult ostracods, which calcify their valves during the cold season, display the highest δ18O values. This is because an increase in water temperature leads to a decrease in fractionation between carbonate and water, and therefore to a decrease in carbonate δ18O. At the same time, an increase in air temperature leads to an increase in the δ18O of lake water through its effect on precipitation δ18O and on evaporation from the lake, and consequently to an increase in carbonate δ18O, opposite to the effect of increasing water temperature on oxygen-isotope fractionation. However, the seasonal and inter-annual variability in lake water δ18O is small (~0.5 ‰) due to the long water residence time of the lake. Seasonal changes in the temperature-dependent fractionation are therefore the dominant cause of carbonate δ18O differences between species when vital offsets are corrected. Temperature reconstructions based on paleotemperature equations for equilibrium carbonate precipitation using the mean δ18O of each species and the mean δ18O of lake water are well in agreement with the observed seasonal water temperature range. The high carbonate δ18O variability of samples within a species, on the other hand, leads to a large scatter in the reconstructed temperatures based on individual samples. This implies that care must be taken to obtain a representative sample size for paleotemperature reconstructions.

A modern snapshot of the isotopic composition of lacustrine biogenic carbonates: Records of seasonal water temperature variability

<p>Carbonate shells and encrustations from lacustrine organisms provide proxy records of past environmental and climatic changes. The oxygen isotopic composition (δ<sup>18</sup>O) of such carbonates depends on water temperature during carbonate precipitation, and on the δ<sup>18</sup>O of the lake water. Lake water δ<sup>18</sup>O, in turn, is controlled by the δ<sup>18</sup>O of precipitation in the catchment, water residence time and mixing, and by evaporation. A paleoclimate interpretation of carbonate δ<sup>18</sup>O records requires a site-specific calibration based on an understanding of the local conditions.</p><p>For this study, carbonates and water were sampled in the littoral zone of lake Locknesjön, central Sweden (62.99°N, 14.85°E, 328 m a.s.l.) along a water depth gradient from 1 to 8 m. We took samples from living organisms and sub-recent samples in surface sediments of the calcifying algae <em>Chara hispida</em>, the mollusk <em>Pisidium</em>, and adult and juvenile instars of two ostracod species, <em>Candona candida</em> and <em>Candona neglecta</em>.</p><p>We show that neither the δ<sup>18</sup>O of carbonates nor the δ<sup>18</sup>O of water vary significantly with water depth, indicating a well-mixed epilimnion. The largest differences in the mean carbonate δ<sup>18</sup>O between species are caused by vital offsets, i.e. the species-specific deviation from the δ<sup>18</sup>O of inorganic carbonate which would have been precipitated in isotopic equilibrium with the water. After subtraction of these constant vital offsets, remaining differences in the mean carbonate δ<sup>18</sup>O between species can mainly be attributed to seasonal water temperature changes. The lowest δ<sup>18</sup>O values are observed in <em>C</em><em>h</em><em>ara</em> encrustations, which form during the summer months when photosynthesis is most intense. Adult ostracods, which calcify their valves during the cold season, display the highest δ<sup>18</sup>O values. This is because an increase in temperature leads to a decrease in fractionation between carbonate and water, and therefore to a decrease in carbonate δ<sup>18</sup>O. An increase in temperature also leads to an increase in the δ<sup>18</sup>O of lake water through its effect on precipitation δ<sup>18</sup>O and on evaporation, and consequently to an increase in carbonate δ<sup>18</sup>O, opposite to the temperature effect on fractionation. However, the seasonal and inter-annual variability in lake water δ<sup>18</sup>O is small (0.5‰) due to the long water residence time. Seasonal changes in the temperature-dependent fractionation are therefore the dominant cause of carbonate δ<sup>18</sup>O differences between species.</p><p>Temperature reconstructions based on “paleo-temperature” equations for equilibrium carbonate precipitation using the mean δ<sup>18</sup>O of each species and the mean δ<sup>18</sup>O of lake water are well in agreement with the observed seasonal water temperature range. The high carbonate δ<sup>18</sup>O variability of samples within a species, on the other hand, leads to a large scatter in the reconstructed temperatures based on individual samples. This implies that care must be taken to obtain a representative sample size for paleo-temperature reconstructions.</p>

Residence Time in Hyporheic Bioactive Layers Explains Nutrient Uptake in Streams

<p>Human activities negatively impact water quality by supplying excessive nutrients to streams. To investigate the capacity of streams to take up nutrients from the water column, we usually add nutrients to stream reaches, calculate the fraction of added nutrients that is taken up, and identify the environmental conditions controlling nutrient uptake. A common idea is that nutrient uptake increases with increasing water residence time because of increased contact time between solutes and organisms. Yet, water residence time only partially explains the temporal and spatial variability of nutrient uptake, and the reasons behind this variability are still not well understood. In this talk I’ll present a study which shows that good characterization of spatial heterogeneity of surface-subsurface flow paths and bioactive hot spots within streams is essential to understanding the mechanisms of in-stream nutrient uptake. The basis of this study arises from the use and interpretation of nutrient uptake results from the Tracer Additions for Spiraling Curve Characterization (TASCC) method. This model has been rapidly adopted to interpret in-stream nutrient spiraling metrics (e.g, nutrient uptake) over a range of concentrations from breakthrough curves (BTCs) obtained during pulse solute injection experiments. TASCC analyses often identify hysteresis in the relationship between spiraling metrics and concentration as nutrient concentration in BTCs rises and falls. The mechanisms behind these hysteresis patterns have yet to be determined. We hypothesized that difference in the time a solute is exposed to bioactive environments (i.e., biophysical opportunity) between the rising and falling limbs of BTCs causes hysteresis in TASCCs. We tested this hypothesis using nitrate empirical data from a solute addition combined with a process-based particle-tracking model representing travel times and transformations along each flow path in the water column and hyporheic zone, from which the bioactive zone comprised only a thin superficial layer. In-stream nitrate uptake was controlled by hyporheic exchange and the cumulative time nitrate spend in the bioactive layer. This bioactive residence time generally increased from the rising to the falling limb of the BTC, systematically generating hysteresis in the TASCC curves. Hysteresis decreased when nutrient uptake primarily occurred in the water column compared to the hyporheic zone, and with increasing the distance between the injection and sampling points. Hysteresis increased with the depth of the hyporheic bioactive layer. Our results indicate that the organisms responsible for nutrient uptake are confined within a thin layer in the stream sediments and that the bioactive residence time at the surface-subsurface water interface is important for nutrient uptake. I will end the talk illustrating how these findings can have important implications for in-stream nutrient uptake within the context of restoration practices addressed to modify the hydro-morphological characteristics of stream channels.</p>