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ABSTRACTThe Andalusian International University held a workshop entitled Temporary wetlands’ future in drylands under the projected global change scenarioin March 2020 in Baeza, Spain, with 26 participants from 10 countries. The workshop objectives were to promote international cooperation and scientific exchange on the conservation and protection of temporary wetlands. The participants highlighted the extreme conditions that temporary and permanent wetlands, ponds, and shallow lakes are currently facing and predicted a dismal future for these systems due to climate change. To foster a holistic view of these ecosystems, the workshop included wetland watersheds. It was concluded that the main threats are those affecting water quality and quantity as well as egg-seed banks, species population dynamics, and food webs. The inherent characteristics of waterbodies in drylands, including high resilience and resistance to harsh conditions, are already negatively impacted by direct human actions and climate change. Another threat is the time lag between scientific warnings about threats and the social and political concern leading to mitigating actions. Thus, more effective actions to protect and conserve temporary wetlands are essential. Research networks could help stimulate the necessary conservation actions, but the global recession due to the COVID-19 pandemic will pose a challenge as economies are burdened with urgent expenditure. This special issue of the journal Inland Watersis the outcome of the workshop presentations and is composed of the ensuing papers on wetlands in drylands.

Acidification diminishes diversity, biomass, and changes aquatic communities by direct and indirect impacts. Changes in the interspecific competition under acidification would alter the aquatic-system community structure in the projected future scenarios. The aim of the present study was to assess the effects of CO2-mediated acidification on two zooplankton species and its impact on the ecological relationship between them. Copepod, Metacyclops minutus, and cladoceran, Daphnia magna, which compete for food and coexist in freshwater ecosystems, were exposed to CO2 injection conditions in monoculture (single species) and polyculture (both species) for 33 days. Three replicates of each treatment (control, pH 6.5, mono and polyculture) were maintained under laboratory-controlled conditions. Population growth rate and carrying capacity were selected as population endpoints. Differences in M. minutus population response under high CO2 concentration led to a positive effect on the abundance of copepod population in polyculture condition, while D. magna showed lower abundance. Despite the higher abundance of copepods under acidification in polyculture condition, in terms of biomass, cladocerans were still dominant by the end of the experimental period. The results highlight the need to consider interspecific interactions when evaluating the harmful effects of acidification, especially in conservation decision-making.

ABSTRACTDrought is an important driver of change in aquatic ecosystems and generally acts as a filter to select biological traits capable of persisting under severe environmental circumstances. Drylands are highly vulnerable to climate change and increases in climate variability. Consequently, an increase in the processes of eutrophication, salinization, and habitat desiccation may be observed in response to the loss of the hydrological connectivity. The International Network on Limnology of Drylands (INLD) was created with the overall goal of understanding the functioning and conservation status of aquatic ecosystems in drylands globally. INLD was made official in 2016 through the International Society of Limnology. Its objectives are to (1) assess the current state of biological diversity in dryland aquatic ecosystems, (2) evaluate the multiple environmental stressors acting in drylands, and (3) develop models to predict effects of global change on drylands. This special issue, Limnology of Drylands, consists of 10 manuscripts focused on the effects of environmental pressures, including global warming, on the biodiversity and distribution of aquatic communities in drylands.

Intensive agriculture is the leading perturbation on freshwater ecosystems due to the agrochemical inputs that compromise biodiversity and ecosystem services. The importance of agriculture cannot be neglected nor the fact that freshwater biodiversity is being depleted worldwide owing to anthropogenic pressures. Therefore, a balance between economic and environmental values must be achieved. The present experiment explores the EEC legal limits on the concentration of agrochemicals (nitrate used as fertilizer) and investigates if even when assuming safe limits there are impacts in freshwater ecosystems. The objective is to assess direct and indirect effects of legal toxicant concentrations on the ecological integrity of plankton communities. This information seeks to assist policy makers with more ecological relevant results to establish legal thresholds that neither overestimates nor underestimates environmental risks. Microcosm experiments were set up outdoors with local assemblages of plankton for 8 weeks. Two nitrate treatments were established: (1) a low treatment (L) of 25 mg l–1 of nitrate, and (2) a high treatment (H) of 50 mg l–1 of nitrate. In conclusion, firstly, we detected that zooplankton taxa shifted from a cladocera-dominated to a copepod-dominated community as an indirect response to phytoplankton decrease. Secondly, both L and H treatments had a negative effect on the plankton community in spite of being within assumed safe legal limits.

The settling flux and content of organic carbon (C), organic matter, and different phosphorus (P) fractions were measured fortnightly during a 6-month stratified period (from early April to early November) with sediment traps located at five different depths in La Concepcion, a mesotrophic and P-limited reservoir in southern Spain. Characterisation of P fractions in the collected material was performed by a sequential extraction procedure. Sedimentation rates exhibited a distinct seasonal pattern, that allowed us to differentiate three periods: (1) a biogenic sedimentation period (BS), in which the sedimentation rates and total suspended matter concentration were lowest and the result of material of autochthonous origin; (2) a calcium carbonate precipitation period (CCP), in which there were high calcium concentrations in the settling seston; and (3) a rainfall period (R), in which the highest sedimentation rates occurred. Organic C, organic matter, and organic P content were highest in the settling material during the BS period and lowest during the R period. However, during the R period, inorganic-P sedimentation rates were highest and the major P fraction was apatite-P. Total organic, and inorganic (Fe- and Al-bound and apatite) P, increased substantially, whereas total and organic C decreased with depth in the material collected by sediment traps during the BS and CCP periods. Consequently, the total C:P (Ct:Pt) and organic C:P (Corg:Porg) ratios decreased significantly with increasing depth of sediment traps.