Modelling interactive effects of multiple disturbances on a coastal lake ecosystem: Implications for management

Phosphorus stoichiometric homeostasis of submerged macrophytes and associations with interspecific interactions and community stability in Erhai Lake, China

According to stoichiometric homeostasis theory, eutrophication is expected to increase the dominance of submerged macrophytes with low homeostatic regulation coefficients (H) relative to those with high H values, ultimately reducing macrophyte community stability. However, empirical evidence supporting this hypothesis is limited. In this study, we conducted a three-year tracking survey (seven sampling events) at 81 locations across three regions of Erhai Lake. We assessed the H values of submerged macrophyte species, revealing significant H values for phosphorus (P) and strong associations of HP values (range: 1.58-2.94) with species and community stability. Moreover, in plots simultaneously containing the dominant high-HP species, Potamogeton maackianus, and its low-HP counterpart, Ceratophyllum demersum, we explored the relationships among eutrophication, interspecific interaction shifts, and community dynamics. As the environmental P concentration increased, the dominance of P. maackianus decreased, while that of C. demersum increased. This shift coincided with reductions in community HP and stability. Our study underpins the effectiveness of H values for forecasting interspecific interactions among submerged macrophytes, thereby clarifying how eutrophication contributes to the decline in stability of the submerged macrophyte community.

Small Mediterranean coastal Lagoons Under Threat: Hydro-ecological Disturbances and Local Anthropogenic Pressures (Size Matters)

Mediterranean coastal lagoons are affected by multiple threats (demographic pressures, eutrophication, climate change) expected to increase in the future and impact the ecosystem services provided. Conservation norms and scientific studies usually focus on large lagoons (> 0.5 km2) due to their economic importance, while they ignore smaller lagoons. These are poorly understood and often unprotected, despite their prevalence within the Mediterranean region and their importance. Qualitative and quantitative characterisation of small lagoons, in terms of functioning and sensitivity to global and local changes, are needed to develop appropriate management strategies. For this purpose, this work provides the first inventory of all Corsican lagoons and has investigated three of them of small size (Arasu, Santa Giulia, Balistra), characterised by contrasting anthropogenic contexts (highly modified/disturbed, medium disturbance, quasi-pristine). At the regional level, 91 of the 95 lagoons identified are < 0.5 km2, making Corsica a good example for the study of small Mediterranean lagoons. The three case studies showed differences in their seasonal biogeochemical cycles and phytoplankton communities (biomass, diversity, photosynthetic efficiency). Arasu and Santa Giulia lagoons showed an increase in watershed urbanisation (+ 12% and + 6% in 30 years), high phytoplankton biomass, low diversity and blooms of potentially harmful dinoflagellates. Conversely, Balistra lagoon showed a good status overall, but some anthropogenic pollution sources within its watershed. This study demonstrates the importance of small lagoons at regional and Mediterranean scale, and provides knowledge on studied local sites but also potential applications elsewhere. The importance of an integrated approach considering lagoons within their adjacent connected systems (watershed and sea) and anthropogenic contexts is highlighted.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12237-023-01182-1.

The challenge of assessing the proper functioning conditions of coastal lagoons to improve their future management

The sustainable management of coastal lagoon hydrosystems is a key issue for the socio-economic and environmental development of many coastal areas worldwide. Often maintained by direct or indirect groundwater supplies, they provide a large range of ecosystem services, from which human societies take advantage. Twenty years after its implementation, a large majority of the Mediterranean lagoons have still not reached the "good status" required by the WFD. Several questions then arise as to the representativeness of the WFD indicators or the relevance of the restoration objectives considering the complexity, evolutionary and unpredictable nature of lagoon hydrosystems. This study proposes an innovative, multidisciplinary, long-term approach to define the proper functioning conditions of a costal lagoon hydrosystems, i.e. all the factors that contribute to the functioning of coastal lagoon hydrosystems and the connectivity with other biodiversity reservoirs, be they ecological, hydrological, social or political. By considering the lagoons and all its hydrological, ecological and societal proper functioning conditions over almost 200 years, this approach makes it possible to assess the influence of past natural and anthropogenic disturbances and support the implementation of future relevant hydrosystem-based management plans which have to be coordinated and politically driven. Defining proper restoration and management objectives should ensure that ecological functions are maintained based on current and future ecosystem benefits and uses. Considering the highly unpredictable nature of coastal hydrosystems, the state of an ecosystem should not only be evaluated on ecological or chemical criteria but also take into account socio-economic and political indicators. The implementation of the 3rd river basin management plan of the WFD as soon as 2022 could be the appropriate occasion to reassess the restoration objectives towards more realistic goals and to give more significance to the definition of the "resilience capacity" of water bodies in place of inappropriate restricted restauration objectives.