Anthropogenic nitrogen pollution in mangrove ecosystems along Dar es Salaam and Bagamoyo coasts in Tanzania

Reviewing the interdecadal dynamics of micropollutants in the Tanzanian coastal zone from 2002 to 2022

The Tanzanian coast is a vastly diversified ecosystem offering ecological, cultural, and economic services. However, anthropogenic and environmental stressors threaten its productivity and sustainability, prompting extensive research to understand the contamination extent, sources, and impacts. This review covers 77 original field research studies published between 2002 and 2022, focusing on the Tanzanian coastal area. A summary of information on the occurrences, levels, distributions, sources, and impacts of organic and inorganic micropollutants in environmental and biological compartments is provided. The studies were further discussed based on their research focus, where seven key areas were identified, which included the types of micropollutants analyzed, the parameters sampled, the locations investigated, and the crucial conclusions reached. The aim was to evaluate the research trends and identify gaps for future investigations. The studies reveal varying contamination levels, from low to severe, encompassing metals, persistent organic pollutants, pesticide residues, nutrients, and microbial contaminants. However, data gaps exist for micropollutant concentrations in ambient air, microplastics, pharmaceuticals, and emerging contaminants of concern. With increasing urbanization and socio-economic activities, the review emphasizes the necessity for solution-based research to remove and control micropollutants in the area. Addressing these challenges is crucial for sustaining the diverse ecological nature of this vital coastal system.

Anthropogenic nitrogen pollution inferred by stable isotope records of crustose coralline algae

Since reef ecosystems can offer intricate habitats for various marine organisms, calcified reefs may contain valuable long-term environmental data. This study investigated stable isotopic composition of marine organisms from the Taoyuan and Linshanbi crustose coralline algae (CCA) reef ecosystems to understand sewage pollution. CCA samples from Taoyuan (Palaeo Xin A: ∼1000 years old and Palaeo G: ∼7000 years old) and Linshanbi (Palaeo L: ∼7000 years old and modern CCA) had significantly lower δ15N values (2.5-5.6 ‰) compared to modern CCA from Taoyuan (10.2 ± 1.2 ‰). Intertidal organisms from the Taoyuan CCA reef also showed higher δ15N values than those from Linshanbi CCA reef, indicating anthropogenic stress in both ecosystems. Long-term pollution monitoring and effective strategies to mitigate sewage pollution are recommended for these CCA reef ecosystems.

Spatial efficiency of protected mangrove areas in Madagascar

Protected Areas (PAs) are an important nature-based solution for mangrove conservation and rehabilitation. We evaluated spatial effectiveness of PAs for mangroves toward achieving Global Conservation Targets (GCTs). The hypothesis for this study was that PAs with different attributes have insignificant effects on mangrove conservation. We assessed the proportions of the most vulnerable mangroves inside PAs, and focused on a typical mangrove country (Madagascar). First, based on remote sensing technology and big data in Google Earth Engine (GEE), we identified the exposure location of mangroves, and determined the environmental factors significantly influencing mangrove distribution. Then, Vulnerability Assessment and Hot-Spot Analysis models were used to measure spatial vulnerability and hotspots of those values, respectively. Finally, we implemented the statistics for the most vulnerable mangroves inside PAs. It was found that: i. Mangroves were mainly abundant in west and east coasts with low latitudes, and the most typical environmental factor influencing mangrove distribution was elevation and; ii. PAs sheltered 486.18 km² (22.16%) of the most vulnerable mangroves in Madagascar. Overall, PAs in Madagascar failed to match 30% of spatial requirements proposed by GCTs (A key proportion of spatial requirements used to reverse trends in biodiversity loss). This study provides a quantitative paradigm for verifying the spatial efficiency of PAs, and will inform local decision-makers on places where mangroves are facing adaption loss to optimize mangrove conservation in future.

Are stable isotopes an efficient tool for tracking the effect of anthropogenic activities on mangrove food web structure and function?

Understanding and connecting the impact of anthropogenic activities on mangrove food webs is a research challenge. Has research on the subject been able to find answers using stable isotopes? The present opinion paper analyzed the utility of stable isotopes in tracing the impact of anthropogenic activities on mangrove food webs and if the research questions raised could be answered using these chemical markers. Representative research papers (16) focused on the use of stable isotopes (δ¹³C, δ¹⁵N, δ³⁴S, δ²H, δD,206Pb/207Pb, and 208Pb/207Pb) to evaluate the effect of anthropogenic activities (Sewage discharge, timber harvesting-deforestation, metallurgical activities, hydrological disruption, aquaculture ponds, and urban development) on mangrove food webs were selected. Each article included at least one group of consumers (invertebrate or fish). Publications only focused on water quality or primary producers were not included. Most studies managed to determine the effect of the anthropogenic activities on the food web's stable isotope values. Based on the above, we concluded that these markers are an effective tool to determine affectation patterns on the structure and function of mangrove food webs. The results obtained herein facilitate the correct management of mangroves and their derived resources.

GIS Multimedia Technology in Regional Construction Land Suitability Evaluation in Mountainous Villages and Towns

In order to explore the suitability evaluation of regional construction land in mountainous villages and towns, a method based on GIS technology is proposed. Supported by GIS and RS technology, the Delphi method is used to determine the natural, socioeconomic, and ecological security factors affecting the ecological suitability of regional construction land in mountainous villages and towns, and analytic hierarchy process is used to calculate the weight of relevant influencing factors. Following the principle of giving priority to ecological protection, a set of ecological suitability evaluation model system and method of regional construction land in mountainous villages and towns are established, based on which the basic ecological control areas of mountainous villages and towns in the study area are divided, so as to provide suggestions for rational and effective planning of land resources in mountainous villages and towns. The experimental results show that the K-means clustering method is divided into five categories: the most suitable land, the more suitable land, the basically suitable land, the unsuitable land, and the unavailable land. Finally, according to the suitability grade system of construction land, it is reclassified, the unsuitable land and unavailable land are divided into basic ecological control areas, the most suitable land and more suitable land are divided into construction control areas, and the basically suitable land is listed as ecological buffer areas. It is proved that the basic ecological control area determined by the model method is basically consistent with the current basic ecological control line of a city, which shows that the model is practical and scientific.

Diluted Seawater and Ammonia-N Tolerance of Two Mangrove Crab Species. New Insights to Understand the Vulnerability of Pristine Islands Ecosystems Organisms

Mangrove ecosystems are the primary receptors of anthropogenic pollution in tropical areas. Assessing the vulnerability of these ecosystems can be expressed, among other indicators, by studying the health of ‘ecosystem engineers’. In this study, mangrove forests facing opposing anthropogenic pressures were studied (i) in the uninhabited island of Europa (Mozambique Channel), considered as a pristine ecosystem, and, (ii) on the island of Mayotte, facing regular domestic wastewater discharges. Using an ecophysiological approach, the effects of diluted seawater (DSW) and increased ammonia-N were studied for two fiddler crab species: Gelasimus tetragonon (GT) on the island of Europa and Paraleptuca chlorophthalmus (PC) on the island of Mayotte. Osmoregulation curves and osmoregulatory capacity were determined along with O2 consumption rates after a 96 h exposure period. Histological analyses were also carried out on two important metabolic organs: the hepatopancreas and the posterior gills. Results indicate that both crab species are good hyper-hypo-osmoregulators but only PC can maintain its osmoregulatory capacity when exposed to ammonia-N. Oxygen consumption is increased in GT after 96 h of exposure to ammonia-N but this does not occur in PC. Finally, a thickening of the gill osmoregulatory epithelium was observed after 96 h in PC when exposed to ammonium but not in GT. Therefore, the two species do not have the same tolerance to DSW and increased ammonia-N. PC shows physiological acclimation capacities in order to better manage nitrogenous enrichments. GT did not show the same physiological plasticity when exposed to ammonia-N and could be more at risk by this kind of stress. These results along with those from other studies regarding the effects of domestic effluents on mangrove crabs are discussed. Therefore, the greater vulnerability of organisms occupying pristine ecosystems could induce major changes in mangrove functioning if crabs, that are engineer species of the ecosystem, are about to reduce their bioturbation activity or, even, disappear from the mangrove forests.