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Urbanization is occurring at a rapid pace in developing countries. The urban stream syndrome has been well documented in higher-income countries, but in lower-income, developing countries, resources often are unavailable for quantifying how urbanization affects streams. Basic infrastructure to support water supply and wastewater treatment frequently is lacking in lower-income countries, and this situation has repercussions for human health and for ecosystem structure and function. The interaction of environmental, social, and economic factors may produce differences in the expression of the urban stream syndrome in lower-income countries relative to in high-income countries. We address how patterns of economic development and urbanization can influence the quality of freshwater resources, and we discuss some of the relationships between urban watersheds and marginalized human populations in lower-income countries. We argue that sustainable management of urban watersheds and the provisioning of drinking water and sanitation services require integration of innovative technology and financing schemes into ecosystem-based management. We must develop new and enhance existing uses for sewage and other wastewater to support ecologically functional urban watersheds. Furthermore, managers of freshwater resources in lower-income countries require more data on which to base decisions. Acquisition of these data will necessitate the creation of interdisciplinary research teams with representatives from national and international development organizations to address stakeholder-driven research questions.

The species Chironomus sp. “Florida” has several qualities that make it a potential aquatic laboratory model to be used in Puerto Rico. Its use as such, however, requires a rearing protocol and life cycle description not previously reported. The present study addresses this lack of information by first describing a rearing method obtained through three years of observations. Next we describe and discuss the life cycle and the effects of temperature and feeding on development. The species has a short life cycle (typically 11 days) and larval stages easily identified using body measurements. Temperature affects the duration of the life cycle, with warm temperatures producing faster development than cold temperatures. The effects of different food concentrations vary: in large water volumes, concentrations of 2 mg/larva/day produce faster developmental times, but at low water volumes, small food concentrations of 0.5 mg/larva/day produce faster developmental times. The rearing protocol and life cycle parameters presented in this study are intended to promote the use of this species as a laboratory model. The fast development of Chironomus sp. “Florida” makes it ideal for toxicological studies.

This paper presents a novel deep neural network for real-time emotion recognition based on facial expression measurement, optimized for low computational complexity, called Lightweight Expression Recognition Network (LiExNet). The LiExNet architecture comprises only 42,000 parameters and integrates convolutional layers, depthwise convolutional layers, an efficient channel attention mechanism, and fully connected layers. The network was trained and evaluated on three widely used datasets (CK+, KDEF, and FER2013) and a custom dataset, EMOTION-ITCH. This dataset comprises facial expressions from both industrial workers and non-workers, enabling the study of emotional responses to occupational stress. Experimental results demonstrate that LiExNet achieves high recognition performance with minimal computational resources, reaching 99.5% accuracy on CK+, 88.2% on KDEF, 79.2% on FER2013, and 96% on EMOTION-ITCH. In addition, LiExNet supports real-time inference on embedded systems, requiring only 0.03 MB of memory and 1.38 GFLOPs of computational power. Comparative evaluations show that among real-time methods, LiExNet achieves the best results, ranking first on the CK+ and KDEF datasets, and second on FER2013, demonstrating consistent performance across these datasets. These results position LiExNet as a practical and robust alternative for real-time emotion monitoring and emotional dissonance assessment in occupational settings, including hardware-constrained and embedded environments.

The relative importance of allochthonous and autochthonous resources in fueling tropical headwater streams remains an open topic. We combined estimates of secondary production and assessment of its trophic basis to determine which resources were responsible for animal production. We studied benthic insect assemblages in two streams in the Luquillo Experimental Forest, Puerto Rico. Habitat-weighted production estimates were similar in both streams (528.5 and 591.5 mg m−2 year−1), but production was over twice as high in pool versus riffle habitats. The mayfly Neohagenulus (Leptophlebiidae) was a major contributor to total production (259.1 and 352.2 mg m−2 year−1). All taxa relied heavily on amorphous detritus and plant tissue. Aquatic insect production was similar to that reported for shrimp assemblages in the same study area, but low relative to temperate region estimates. The trophic basis of production appears to be allochthonous organic matter, which agrees with the small size and closed canopy cover over the study streams. This is the first study quantifying the production and trophic basis of the non-shrimp macroinvertebrate assemblage in tropical island streams. We also provide support for the importance of riparian vegetation as the main energy sources for stream tropical stream food webs.

The exchange of nutrients and organic material that occurs along the riparian zones of stream ecosystems is vital to providing energetic subsidies for both aquatic and terrestrial food webs. Orb-weaver spiders are major consumers of emerging aquatic insects, so impacts to the stream ecosystem and the riparian zone around it can have significant effects on riparian spider assemblages. Aquatic insects can represent anywhere from ∼50–100% of the diet of riparian orb-weavers, generally depending on factors such as spider taxa and prey diversity. However, most of the studies that examine riparian orb-weaver diets have been done in non-urban areas. Thus, little is known about how urbanization affects the transfer of energy and nutrients between aquatic and terrestrial ecosystems. The objective of our study was to determine if the proportion of aquatic insects in the diets of riparian orb-weaver spiders is altered by urbanization. We used stable isotope analyses and Bayesian mixing models to assess trophic transfers between primary energy sources, insects, and orb-weaver spiders along the riparian zone of an urban gradient in San Juan, Puerto Rico. We found that both δ13C and δ15N values varied with the amount of urbanization in aquatic insects, terrestrial insects, and 2 genera of riparian orb-weaver spiders. Spiders closely reflected changes in the isotopic values observed in aquatic insects along the urban gradient, with a noticeable decrease in δ15N values at the most urbanized sites. In addition, we found that the proportion of aquatic insects in the diets of the orb-weavers was ∼30% greater in heavily urbanized areas than non-urbanized areas. This study represents one of the few efforts to determine how urbanization can significantly alter riparian food webs and influence the exchange of subsidies between aquatic and terrestrial ecosystems.

Understanding how environmental variables influence the distribution and density of organisms over relatively long temporal scales is a central question in ecology given increased climatic variability (e.g., precipitation, ENSO events). The primary goal of our study was to evaluate long-term (15y time span) patterns of climate, as well as environmental parameters in two Neotropical streams in lowland Costa Rica, to assess potential effects on aquatic macroinvertebrates. We also examined the relative effects of an 8y whole-stream P-enrichment experiment on macroinvertebrate assemblages against the backdrop of this long-term study. Climate, environmental variables and macroinvertebrate samples were measured monthly for 7y and then quarterly for an additional 8y in each stream. Temporal patterns in climatic and environmental variables showed high variability over time, without clear inter-annual or intra-annual patterns. Macroinvertebrate richness and abundance decreased with increasing discharge and was positively related to the number of days since the last high discharge event. Findings show that fluctuations in stream physicochemistry and macroinvertebrate assemblage structure are ultimately the result of large-scale climatic phenomena, such as ENSO events, while the 8y P-enrichment did not appear to affect macroinvertebrates. Our study demonstrates that Neotropical lowland streams are highly dynamic and not as stable as is commonly presumed, with high intra- and inter-annual variability in environmental parameters that change the structure and composition of freshwater macroinvertebrate assemblages.

Meiofauna is a group of heterotrophic organisms smaller than macroinvertebrates but larger than microfauna and characterized by groups such as testate amoebae, ciliates, and nematodes. They are a link between bacteria and resources and macroinvertebrates. However, tropical meiofauna is poorly studied; thus, our goal was to characterize meiofaunal community composition and abundance and assess potential environmental variables controlling these community dynamics. Monthly samplings of meiofauna were conducted for eight months in Quebrada Prieta, El Yunque National Forest, Puerto Rico. Sampling was made in 12 pools, and data on discharge, sediment characteristics, and biotic variables were also collected. A total of 62 meiofaunal morphospecies were identified, with nematodes dominating the community, followed by testate amoebae. Bacterivores and detritivores taxa dominated the community. Meiofaunal abundance was negatively related to discharge and positively to the percentage of coarse sand, nitrate, and macroinvertebrate abundance. The composition of meiofauna in Quebrada Prieta is like the composition reported for temperate streams, at least in major meiofaunal groups present. However, the community in Quebrada Prieta was dominated by testate amoebae. In contrast, temperate streams are often dominated by rotifers and nematodes. Both abiotic and biotic variables are important for meiofaunal communities in the headwater streams in Puerto Rico.

Nutrient inputs to surface waters are particularly varied in urban areas, due to multiple nutrient sources and complex hydrologic pathways. Because of their close proximity to coastal waters, nutrient delivery from many urban areas can have profound impacts on coastal ecology. Relatively little is known about the temporal and spatial variability in stoichiometry of inorganic nutrients such as dissolved silica, nitrogen, and phosphorus (Si, N, and P) and dissolved organic matter in tropical urban environments. We examined nutrient stoichiometry of both inorganic nutrients and organic matter in an urban watershed in Puerto Rico served by municipal sanitary sewers and compared it to two nearby forested catchments using samples collected weekly from each river for 6 yr. Urbanization caused large increases in the concentration and flux of nitrogen and phosphorus (2- to 50-fold), but surprisingly little change in N:P ratio. Concentrations of almost all major ions and dissolved silica were also significantly higher in the urban river than the wildland rivers. Yield of dissolved organic carbon (DOC) was not increased dramatically by urbanization, but the composition of dissolved organic matter shifted toward N-rich material, with a larger increase in dissolved organic nitrogen (DON) than DOC. The molar ratio of DOC:DON was about 40 in rivers draining forested catchments but was only 10 in the urban river. Inclusion of Si in the assessment of urbanization’s impacts reveals a large shift in the stoichiometry (Si:N and Si:P) of nutrient inputs. Because both Si concentrations and watershed exports are high in streams and rivers from many humid tropical catchments with siliceous bedrock, even the large increases in N and P exported from urban catchments result in delivery of Si, N, and P to coastal waters in stoichiometric ratios that are well in excess of the Si requirements of marine diatoms. Our data suggest that dissolved Si, often neglected in watershed biogeochemistry, should be included in studies of urban as well as less developed watersheds due to its potential significance for marine and lacustrine productivity.

High abundance of trees capable of biological N-fixation (henceforth “N-fixers”) in tropical forests has been hypothesized to drive higher stream nitrate (NO3) concentrations compared to temperate counterparts. However, to date there have been no empirical linkages of stream NO3 concentrations with the productivity of tropical forests. Here, we combined three unique long-term datasets from La Selva Biological Station, Costa Rica: 21 years of (1) mean annual stream NO3-N concentrations in six stream sites within the same watershed, (2) annual growth of trees, and (3) annual leaf litterfall. We hypothesized that years of greater growth of N-fixer tree species and of greater leaf litterfall would be correlated with higher stream water NO3-N concentrations. We also hypothesized that landscape position mediates these relationships, with growth of N-fixer trees on adjacent slopes being more strongly correlated to stream NO3-N than the growth of such trees on upland plateau sites. We found that mean annual stream NO3-N concentrations were consistently high (160–260 µg L−1). There was substantial interannual variation in leaf litterfall (inter-year range: 5.4 to 8.1 Mg ha−1 year−1), growth of N-fixers (inter-year range: 1.2 to 2.2 Mg ha−1 year−1), and growth of all other tree species (inter-year range: 2.1 to 3.2 Mg ha−1 year−1). To assess stream NO3-N relationships with forest productivity, we used water conductivity to account for dilution resulting from variable discharge. We found that NO3-N concentrations were positively related to the annual growth of the N-fixers on nearby slopes, and were negatively correlated with annual leaf litterfall. Stream NO3-N concentrations were not related to the growth of N-fixers or other tree species in the more removed plateau areas. Using a mass balance, we estimated that symbiotic N fixation can account for 7–29% of NO3 export. Both the growth of adjacent N-fixers and landscape-wide leaf litterfall are important drivers of the inter-annual variability of stream NO3-N concentrations. Our results suggest that predicted changes in precipitation extremes due to climate change will alter N dynamics in tropical forests both directly, by altering discharge and export, and indirectly, by altering N-fixer tree productivity.