Limnological Review

Site-specific ecotoxicological monitoring data on dairy final effluents in karst groundwater environments remain scarce. This preliminary site-specific case study combined physicochemical characterisation with a 24 h Daphnia magna immobilisation assay of three final-effluent samples collected after the complete treatment train in winter, spring and summer. The three sampling occasions were used as independent screening snapshots to test for an acute response at high effluent concentrations, not to estimate the seasonal variability or treatment-stage efficiency. Six effluent exposure groups (three samples × two concentrations) were tested at 80% and 100% (v/v), each in four vessels containing five organisms, together with three negative controls. Across samples, the pH was 8.1–8.4, the temperature was 11.5–26.4 °C, the dissolved oxygen was 7.89–9.75 mg/L, the TSS was 3–9 mg/L, the COD was 16.4–40.4 mg/L and the BOD₅ was 3.3–4.0 mg/L. No immobilisation occurred, and the 24 h EC₅₀ was reported as >100% (v/v); the potassium dichromate EC₅₀ values were 1.07–1.18 mg/L. No detectable 24 h acute immobilisation was observed in any of the three tested final-effluent samples. These findings provide a quantified site-specific final-effluent profile linked to a standardised whole-effluent effect endpoint and indicate the absence of acute immobilisation under the tested conditions.

The phytoplankton community, which forms the base of aquatic food webs, plays a central role in ecosystem functioning and accounts for most primary production in aquatic systems, particularly in lentic environments. However, climate change and chemical pollution, especially herbicides, pose increasing threats to its structure and functioning. We hypothesized that herbicide exposure would alter both structural and functional attributes of the phytoplankton community, with primary production responding more strongly than community structure. This experimental study evaluated the effects of two widely used herbicides, atrazine and 2,4-D, applied individually and in combination, on a phytoplankton community maintained at a fixed elevated temperature representative of the Shared Socioeconomic Pathway SSP2-4.5 scenario described in the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Because temperature was not experimentally varied, the study was designed to assess herbicide responses under this fixed elevated thermal condition rather than warming effects or herbicide–temperature interactions. Phytoplankton samples collected from an artificial urban reservoir were exposed to six treatments, including a control, comprising different nominal concentrations of atrazine (32 and 64 µg L⁻¹) and 2,4-D (150 and 500 µg L⁻¹), applied alone or in mixture, in a completely randomized design with 10 independent replicates per treatment. Throughout the experiment, all samples were maintained under identical experimental conditions: a constant temperature of 31.8 °C, an irradiance of 140 µmol m⁻² s⁻¹, and a 12 h light/12 h dark photoperiod. Response variables included density, taxonomic composition, biomass (chlorophyll a), and primary production (net photosynthesis). The results showed that herbicide treatment altered taxonomic composition and was associated with a marginal response in density but had no significant effects on species richness, diversity, evenness, dominance, or biomass. In contrast, net photosynthesis was the only functional variable significantly affected by herbicide treatments, with post hoc comparisons revealing lower values in the Mixture treatment than in the 2,4-D High treatment. Overall, these findings suggest a decoupling between community structure and phytoplankton functional performance following exposure to atrazine and 2,4-D under a thermal condition representative of the SSP2-4.5 climate scenario, with net photosynthesis appearing more sensitive than conventional structural descriptors.

We tested how depth-linked hydrostatic pressure, sediment temperature, and sediment texture, represented here by grain-size distribution, partition methane (CH₄) between dissolved storage in sediment porewater and ebullitive release in a tropical monomictic lake. Along a shoreline-to-center transect spanning 1.5–7 m depth, we measured 24-h ebullition with replicated inverted funnels over three consecutive days and quantified porewater methane from short cores while recording depth, sediment temperature, grain size, wind, and barometric pressure. Ebullition was greatest at shallow, warmer, sandier sites, whereas porewater methane accumulated at deeper, cooler sites, yielding an inverse spatial pattern of the two phases. Site-level regressions identified sand content as the strongest spatial correlate of bubbling, while porewater methane increased with depth and declined with sediment temperature. Under weak winds and near-constant barometric pressure, ebullition showed no detectable day-to-day variation over the sampled 72-h interval, indicating that between-site differences exceeded short-term temporal variability. Together, these results describe a spatially resolved storage–release pattern consistent with depth-, temperature-, and texture-related controls on methane retention and bubbling in Lake Carioca.