<p>Compound anthropogenic pressures are driving critical mangrove degradation worldwide, threatening the wellbeing of coastal human populations historically associated with these systems. The Ramsar and Biosphere Reserve, Ci&#233;naga Grande de Santa Marta (CGSM) is located in the northern of Colombia and is the largest coastal lagoon-delta in the Caribbean. It is inhabited by stilt communities that have developed intricate livelihood and cultural relationships with the mangroves. The CGSM has experienced sustained social and ecological degradation during the last six decades, triggered by land-use change and disruption of hydrological connections. This study integrates Social-ecological Memory from fishing communities and Paleoenvironmental frameworks to develop a historical perspective of the biophysical and social dimensions of environmental change in the CGSM. Integrating X-ray fluorescence (XRF) geochemical sediment analysis, C<sup>14</sup> radiocarbon dating, and demographic inferences from archaeological evidence revealed three distinct periods over the last ~5000 years where sea-level rise and hydroclimatic variability shaped the transition between freshwater to prevailing marine conditions and modulated human occupation patterns in the area. Specifically, the period with the highest hydroclimatic variability and precipitation minima (4000 &#8211; 2500 yr BP) is consistent with the lowest human population estimates, whereas sea-level increase (~ 2000 yr BP) corresponds with a sustained increase in estimated population growth. In connection, participatory oral reconstructions conducted in the stilt-house communities of Buenavista and Nueva Venecia, offered nuanced descriptions about the spatial, temporal, and contextual aspects generating and reinforcing hypersalinization of the system, and their profound social-ecological consequences over the past several decades. The interdisciplinary approach of this study indicates that the CGSM is a highly dynamic socio-ecological system that has been changing and reconfiguring across different time scales in response to both natural and human-induced processes. Finally, it reveals the relative effects of biophysical and social drivers on driving social-ecological change on millennial to decadal time scales.</p>
Abstract Tropical rivers are dynamic CO 2 sources. Regional patterns in the partial pressure of CO 2 ( p CO 2 ) and relationships with other a/biotic factors in densely populated and rapidly developing river delta regions of Southeast Asia are still poorly constrained. Over one year, at 21 sites across the river system in the Red River Delta (RRD), Vietnam, we calculated p CO 2 levels from temperature, pH, and total alkalinity and inter-linkages between p CO 2 and phytoplankton, water chemistry and seasonality were then assessed. The smaller, more urbanized, and polluted Day River had an annual median p CO 2 of 5000 ± 3300 µ atm and the larger Red River of 2675 ± 2271 µ atm. p CO 2 was 1.6 and 3.2 times higher during the dry season in the Day and Red rivers respectively than the rainy season. Elevated p CO 2 levels in the Day River during the dry season were also 2.4-fold higher than the median value (2811 ± 3577 µ atm) of calculated and direct p CO 2 measurements in >20 sub/tropical rivers. By further categorizing the river data into Hanoi City vs. other less urban-populated provinces, we found significantly higher nutrients, organic matter content, and riverine cyanobacteria during the dry season in the Day River across Hanoi City. Forward selection also identified riverine cyanobacteria and river discharge as the main predictors explaining p CO 2 variation in the RRD. After accounting for the shared effects (14%), river discharge alone significantly explained 12% of the p CO 2 variation, cyanobacteria uniquely a further 21%, while 53% of the p CO 2 variance was unexplained by either. We show that the urbanization of rivers deltas could result in increased sources of riverine p CO 2 , water pollution, and harmful cyanobacterial blooms. Such risks could be mitigated through water management to increase water flows in problem areas during the dry season.
Abstract. Geography and associated hydrological, hydroclimate and land-use conditions and their changes determine the states and dynamics of wetlands and their ecosystem services. The influences of these controls are not limited to just the local scale of each individual wetland but extend over larger landscape areas that integrate multiple wetlands and their total hydrological catchment – the wetlandscape. However, the data and knowledge of conditions and changes over entire wetlandscapes are still scarce, limiting the capacity to accurately understand and manage critical wetland ecosystems and their services under global change. We present a new Wetlandscape Change Information Database (WetCID), consisting of geographic, hydrological, hydroclimate and land-use information and data for 27 wetlandscapes around the world. This combines survey-based local information with geographic shapefiles and gridded datasets of large-scale hydroclimate and land-use conditions and their changes over whole wetlandscapes. Temporally, WetCID contains 30-year time series of data for mean monthly precipitation and temperature and annual land-use conditions. The survey-based site information includes local knowledge on the wetlands, hydrology, hydroclimate and land uses within each wetlandscape and on the availability and accessibility of associated local data. This novel database (available through PANGAEA https://doi.org/10.1594/PANGAEA.907398; Ghajarnia et al., 2019) can support site assessments; cross-regional comparisons; and scenario analyses of the roles and impacts of land use, hydroclimatic and wetland conditions, and changes in whole-wetlandscape functions and ecosystem services.
Macrophyte invasive species spreading is one of the most pressing threats to tropical shallow lakes. Yet, studies addressing the full extent of biotic and abiotic changes that may occur in response to invasive species are poorly documented. Less known is how other human-induced stressors such as eutrophication and lake draining may interact over time with invasive macrophytes to jointly influence biodiversity loss. We combined ecological and limnological observations with paleoecological data from a eutrophic Neotropical shallow lake, Fúquene Lake, Colombia, to provide information on the current and long-term (decades-centuries) dynamics of spread of two well-established invasive plants Eichhornia crassipes and Egeria densa. At present-day, areas dominated by Egeria and Eichhornia were unique in macrophyte structure and differed from those areas having a mixture of macrophyte species or open waters. Eichhornia areas encompassed 14 macrophyte species and had turbid (secchi=19 ±6 cm) and poorly oxygenated (3.94 ±2.61 ppm) waters. Egeria areas had clearer (secchi=51 ±12 cm) and better-oxygenated (6.06 ± 2.4 ppm) waters supporting six macrophyte species. Historical macrophyte community shifts were linked to eutrophication and hydrological alteration exemplify by losses of charophytes and bryophytes before 1500 CE and subsequent reductions in Nymphaea sp., Potamogeton illinoensis and Najas guadalupensis in the early 1900s (lake draining). E. crassipes (since 1500 CE) and E. densa (early 1900s) occurred well before suggested dates of introduction (1950s and 1990 respectively). Yet, they severely expanded since the 1990s along with Azolla filiculoides in response to an inflow waters diversion scheme and heavy nutrient load. Results suggest that the spread of Eichhornia and Egeria was not responsible for historical resident species loss. Nevertheless, their current domination is exerting synergetic and antagonistic secondary effects on plant assemblages through habitat modification, competitive exclusion and promotion of habitat spatial heterogeneity across the lake. Equating macrophyte species loss with invasive plants spreading in degraded lakes could be therefore misleading. Aggressive species like Eichhornia, Azolla and Egeria are suggested to require eutrophic environments to spread, thus, management actions should focus on controlling nutrient load. Our study demonstrates the need of addressing long-term approaches to fully-understanding the effects of invasive macrophyte spread.
Abstract. Geography and associated hydrological, hydroclimate and land use conditions and their changes determine the states and dynamics of wetlands and their ecosystem services. The influences of these controls are not limited to just the local scale of each individual wetland, but extend over larger landscape areas that integrate multiple wetlands and their total hydrological catchment – the wetlandscape. However, the data and knowledge of conditions and changes over entire wetlandscapes are still scarce, limiting the capacity to accurately understand and manage critical wetland ecosystems and their services under global change. We present a new database, consisting of geographic, hydrological, hydroclimate and land use information and data for 27 wetlandscapes around the world. This combines survey-based local information with geographic shapefiles and gridded datasets of large-scale hydroclimate and land use conditions and their changes over whole wetlandscapes. Temporally, the database contains 30-year time series of data for mean monthly precipitation and temperature, and annual land use conditions. The survey-based site information includes local knowledge on the wetlands, hydrology, hydroclimate and land uses within each wetlandscape, and on the availability and accessibility of associated local data. This novel database (available through PANGAEA https://doi.pangaea.de/10.1594/PANGAEA.907398; Ghajarnia et al., 2019) can support site assessments, cross-regional comparisons, and scenario analyses of the roles and impacts of land use, hydroclimatic and wetland conditions and changes on whole-wetlandscape functions and ecosystem services.
Successful plant invasions are hypothesised to be associated with close environmental matching or species poor communities. However, positive correlations between non-native abundance and native plant richness can also arise due to habitat heterogeneity (defined here as variation in abiotic and biotic conditions over space and time). We analysed survey and palaeoecological data for macrophytes in lakes covering a gradient of eutrophication and connectivity to partition the roles of environmental matching, macrophyte diversity and habitat heterogeneity in explaining abundance and invasibility of Elodea canadensis, a widely distributed non-native macrophyte in Europe. There was no association between invasibility and macrophyte species richness. Instead habitat heterogeneity variously enabled the coexistence of native macrophytes and E. canadensis in lake metacommunities over time. Invasion resistance was associated with high native macrophyte cover and unfavourable environmental conditions. We show how spatial and temporal scales can determine the relationship between habitat heterogeneity and invasibility in lake systems.
In November 2004, a regional climate change workshop was held in Guatemala with the goal of analyzing how climate extremes had changed in the region. Scientists from Central America and northern South America brought long‐term daily temperature and precipitation time series from meteorological stations in their countries to the workshop. After undergoing careful quality control procedures and a homogeneity assessment, the data were used to calculate a suite of climate change indices over the 1961–2003 period. Analysis of these indices reveals a general warming trend in the region. The occurrence of extreme warm maximum and minimum temperatures has increased while extremely cold temperature events have decreased. Precipitation indices, despite the large and expected spatial variability, indicate that although no significant increases in the total amount are found, rainfall events are intensifying and the contribution of wet and very wet days are enlarging. Temperature and precipitation indices were correlated with northern and equatorial Atlantic and Pacific Ocean sea surface temperatures. However, those indices having the largest significant trends (percentage of warm days, precipitation intensity, and contribution from very wet days) have low correlations to El Niño–Southern Oscillation. Additionally, precipitation indices show a higher correlation with tropical Atlantic sea surface temperatures.
Tropical river deltas, and the social-ecological systems they sustain, are changing rapidly due to anthropogenic activity and climatic change. Baseline data to inform sustainable management options for resilient deltas is urgently needed and palaeolimnology (reconstructing past conditions from lake or wetland deposits) can provide crucial long-term perspectives needed to identify drivers and rates of change. We review how palaeolimnology can be a valuable tool for resource managers using three current issues facing tropical delta regions: hydrology and sediment supply, salinisation and nutrient pollution. The unique ability of palaeolimnological methods to untangle multiple stressors is also discussed. We demonstrate how palaeolimnology has been used to understand each of these issues, in other aquatic environments, to be incorporated into policy. Palaeolimnology is a key tool to understanding how anthropogenic influences interact with other environmental stressors, providing policymakers and resource managers with a 'big picture' view and possible holistic solutions that can be implemented.
Abstract Eutrophication is commonly implicated in the reduction in macrophyte species richness in shallow lakes. However, the extent to which other more nuanced measures of macrophyte diversity, such as assemblage heterogeneity, are impacted concurrently by eutrophication over space and time and the joint influences of other factors (e.g., species invasions and connectivity) remains relatively poorly documented. Using a combination of contemporary and paleoecological data, we examine how eutrophication influences macrophyte assemblage heterogeneity and how nutrient enrichment interacts with watercourse connectivity, lake surface area, and relative zebra mussel abundance over space (within and among lakes) and time (decades to centuries) at the landscape scale. The study system is the Upper Lough Erne, Northern Ireland, UK , which is composed of a large main lake and several smaller satellite lakes that vary in their hydrological connectivity to the main lake. By applying homogeneity analysis of multivariate dispersions and partial redundancy analysis, we demonstrate that contemporary lake macrophyte heterogeneity and species richness are reduced in lakes with intensified eutrophication but are increased in lakes with greater zebra mussel abundance and lake surface area. Watercourse connectivity positively influenced assemblage heterogeneity and explained larger proportions of the variation in assemblage heterogeneity than local environmental factors, whereas variation in species richness was better related to local abiotic factors. Macrophyte fossil data revealed within‐ and among‐lake assemblage homogenization post‐1960, with the main lake and connected sites showing the highest rates of homogenization due to progressive eutrophication. The long‐term and contemporary data collectively indicate that eutrophication reduces assemblage heterogeneity over time by overriding the importance of regional processes (e.g., connectivity) and exerts stronger pressure on isolated lakes. Our results suggest further that in connected lake systems, assemblage heterogeneity may be impacted more rapidly by eutrophication than species richness. This means that early effects of eutrophication in many systems may be underestimated by monitoring that focuses solely on species richness and is not performed at adequate landscape scales.
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