Global metrics of land cover and land use provide a fundamental basis to examine the spatial variability of human-induced impacts on freshwater ecosystems. However, microscale processes and site ...specific conditions related to bank vegetation, pollution sources, adjacent land use and water uses can have important influences on ecosystem conditions, in particular in smaller tributary rivers. Compared to larger order rivers, these low-order streams and rivers are more numerous, yet often under-monitored. The present study explored the relationship of nutrient concentrations in 150 streams in 57 hydrological basins in South, Central and North America (Buenos Aires, Curitiba, São Paulo, Rio de Janeiro, Mexico City and Vancouver) with macroscale information available from global datasets and microscale data acquired by trained citizen scientists. Average sub-basin phosphate (P-PO4) concentrations were found to be well correlated with sub-basin attributes on both macro and microscales, while the relationships between sub-basin attributes and nitrate (N-NO3) concentrations were limited. A phosphate threshold for eutrophic conditions (>0.1 mg L-1 P-PO4) was exceeded in basins where microscale point source discharge points (eg. residential, industrial, urban/road) were identified in more than 86% of stream reaches monitored by citizen scientists. The presence of bankside vegetation covaried (rho = -0.53) with lower phosphate concentrations in the ecosystems studied. Macroscale information on nutrient loading allowed for a strong separation between basins with and without eutrophic conditions. Most importantly, the combination of macroscale and microscale information acquired increased our ability to explain sub-basin variability of P-PO4 concentrations. The identification of microscale point sources and bank vegetation conditions by citizen scientists provided important information that local authorities could use to improve their management of lower order river ecosystems.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Studies of the effects of landscape configuration on nutrient concentrations in aquatic systems, apart from land cover percentages, remain limited. Understanding these influences is important to ...guide land use planning and avoid the undesirable consequences of artificial eutrophication. We investigated how land use and natural landscape attributes such as edge density, mean shape index, cohesion, and contagion were related to nitrate (N-NO3) and phosphate (P-PO4) concentrations in Brazilian streams and Mexican lakes. Data on nutrient concentrations were collected by citizen science volunteers from 2013 to 2016, and we calculated land use classes and landscape metrics for each watershed. We developed models to predict nutrient concentrations based on landscape metrics, watershed slope, and season after excluding autocorrelated predictors. We used the Generalized Additive Model for Location, Shape and Scale framework and found the distribution (gamma or lognormal) that provided the best fit to the data based on the Akaike Information Criterion. The best predictors were selected following a stepwise strategy. We found relatively high N-NO3 (5–10 mg/L) and P-PO4 (0.5–1.0 mg/L) concentrations in the watersheds in both countries. Landscape composition (percentages of urban and agricultural areas) and configuration (mean shape indexes for urban and agricultural land use) metrics were the key predictors in the model for P-PO4 in Brazilian streams. In Mexican lakes, the predictors of nutrient concentrations were configuration metrics such as contagion and edge density of natural areas for P-PO4, and cohesion of urban areas for N-NO3. Our findings can be used as a starting point for land use planning, as well as for helping managers predict nutrient enrichment in watersheds within existing urban and agricultural areas. Our study highlights the importance of community-based monitoring that supplements regular monitoring initiatives because we were able to use data collected by citizen scientists to assess potential drivers of nutrient pollution and differences between countries.
Food web structure is well known to vary widely among ecosystems. Recent research indicates that there can be a high degree of spatial heterogeneity within ecosystems as well. Xochimilco is a small ...heterogeneous freshwater system that has been transformed into a network of canals, small lakes, and wetlands. Located within Mexico City, this ecosystem has been intensively managed and highly impacted for more than 50 years. This system receives urban and agricultural runoff, with resulting impacts on water quality. The aquatic community is dominated by exotics such as carp (Cyprinus carpio) and tilapia (Oreocrhomis niloticus), though the system still supports endemic species such as the aquatic salamander, axolotl (Ambystoma mexicanum), and crayfish (Cambarellus montezumae), which are both endangered. In this study, we used carbon and nitrogen stable isotopes for the whole food web and gut content analysis from the exotic fishes to describe food web structure in different canals within Xochimilco. There were significant isotopic differences among canals. These differences may result from isotopic baseline differences as well as differences in actual food web structure: both are related to local spatial variation in water quality driven by nutrient inputs and exotic fishes. Within-ecosystem variability is likely to be seen in other perturbed shallow systems as well, and should be explicitly considered in future food web studies.
► We propose a three-tier process for policy planning of urban agro-ecosystems. ► An application to an urban wetland agro-ecosystem within Mexico City is given. ► The wetland agro-ecosystem has a ...non-market value of $15.6–$31.5million USD/ha/y. ► Economic valuation of ecosystem services provides objective policy guidelines.
This paper proposes a three-tier process for supporting policy planning of urban agroecosystems. It comprises the following steps: (i) definition of the agro-environmental unit; (ii) measurement of the non-market values; (iii) estimation of opportunity cost. An application to an urban wetland agro-ecosystem within Mexico City is used for illustrating our methodology. We estimated that the wetland agro-ecosystem has a lower-bound monetary value between $15.6million and $31.5million USD/ha/y. As the land conversion rate is about 3.73ha/y, the opportunity cost would be between $22,300 and $44,900USD/ha/y. Such figures are an objective way to appreciate both the potential enhancement value and the opportunity cost of ecosystem services adjacent to urban areas, providing both urban and environmental policy guidance. We argue that this framework allows for multi-scale analysis and may be applied for other urban ecosystems as well.
In a world where pristine water is becoming scarcer, the need to reuse water becomes imperative. In this context explaining the water quality, purpose fitness and the parameters or conditions of the ...water body to adjust so as to improve its quality, are of great relevance. The goal of the present study was the use of water, riverine, and biodiversity quality indices to assess the condition of the studied urban wetland, since no single index can provide a complete health assessment of a water body. Decision trees were also used to elucidate the best water parameters to mend in order to recover the overall health of the urban wetland. The decision trees identified relevant physicochemical parameters as well as their approximate concentration at which a healthy water environment can be sustained for zooplankton and proved to be a powerful and simple alternative to customary approaches. Suspended particles and phosphates proved to be important parameters with concentrations approximately lower than 88 mg L
−1
and 11 mg L
−1
, respectively, for a good biodiversity index of zooplankton. Ammonia, total coliforms, BOD, nitrates, and sodium were the main parameters that affected the water quality index. The vegetation coverage and its structure were the driving factors in the riverine quality index of the wetland.
Wastewater release in an urban wetland in Mexico City entails discharging complex mixtures of hundreds of chemical substances into the aquatic system. Therefore, in order to identify the most ...important contaminants, a GC–MS screening method coupled with deconvolution software was used. LC
50
values from ECOSAR and Toxic Units were obtained to identify the organic pollutants-of-concern and to pinpoint the most ecotoxic sites. The results showed that, even though the area has intensive farming, agrochemicals are not of concern. Industrial and domestic groups make up from about 30%–66% of the pollutants for all sites. Of the 189 identified substances, 17 were detected 44% of the time and the Toxic Unit showed that terbutol, coprostanol, and hexadecane were capable of generating considerable adverse effects on the aquatic ecosystem. Total Toxic Units for each site exhibited a decreasing trend as they distanced from the urban and agricultural area.
A mixture of identities, livelihoods and a heterogeneous landscape characterizes the communities located in the rural-urban frontier. The perception of the inhabitants of these communities regarding ...environmental and sociocultural change is linked to their livelihoods and land use decisions. We use the case study of the ancient agricultural chinampa system in the Xochimilco wetland of Mexico City to understand the main threats and opportunities for peri-urban agriculture in megacities, where the rapid displacement of agricultural land by formal and informal settlements makes its future uncertain. We used a household survey and semi-structured interviews to understand: 1) the relationship between agriculture and informal urbanization, and 2) the perception of chinampa users, considering those who are engaged in agriculture and those who are not, regarding the factors that favor or limit agriculture. The information from interviews was coded and conceptualized as pull and push factors for peri-urban agriculture. Sociocultural factors were mentioned as the main reasons that push chinampas into agriculture abandonment, such as community erosion due to conflicts and lack of interest from younger generations. However, those that continue to engage in agriculture maintain a historical connection to farming (whether they are from the region or not), and a willingness to adapt to maintain their agricultural livelihood. We find that while some families abandon their agricultural land, new niches become available for migrants from other surrounding rural areas who find opportunities to continue farming in the peri-urban frontier. Our evidence suggests that the loss of peri-urban agriculture is not a linear process towards urbanization, and that the coexistence of housing, agriculture, and livelihood diversification can produce the conditions needed for innovation to encourage peri-urban agriculture.
•Identity, agricultural livelihoods, and farming adaptation are perceived as pull factors for peri-urban agriculture.•Lack of cooperation, distrust, low profits, and water issues are perceived as push factors for peri-urban agriculture.•As younger generations opt out of agriculture, new niches form to take advantage of the proximity to the city.•Push factors that undermine agriculture for locals could act as pull factors for migrant farmers to farm in the city.•Livelihood diversification, land-use multifunctionality, and innovation are ways for peri-urban agriculture to persist.
Citizen science schemes for environmental monitoring generate benefits for scientists by increasing the capacity of scientists to gather information. Citizen scientist monitoring also benefits the ...citizens involved because they acquire a deeper knowledge and understanding of the benefits of ecosystems and the ways that anthropogenic activities affect them. This study details the efforts of a local non-government organization (Restauración Ecológica y Desarrollo A. C.), the Earthwatch Institute, and the Hongkong and Shanghai Banking Corporation’s Water Program to monitor the water quality in the Xochimilco peri-urban wetland, which is threatened by accelerated urbanization. The Xochimilco wetland includes agricultural areas in which raised beds called chinampas are surrounded by canals and small lakes. These chinampas have been managed for hundreds of years. The water in the canals is mainly used for agricultural irrigation, but it is also the habitat of a variety of aquatic species. In this study, we analyze the water quality of 7 canals and 1 lake located in areas with chinampas that have different uses such as housing, tourism, semi-intensive agriculture, agroecological farming, and abandoned agricultural land. Water samples from these sites were collected by citizen scientists over the course of 4 y. Our aim was to determine how the water quality varies across areas with management differences and between dry and rainy seasons. We found significant differences in pH, temperature, dissolved oxygen, Escherichia coli, and conductivity between seasons. We expected to find suitable water quality for irrigation (based on national and international guidelines) in canals near low-impact activities in the chinampas (such as agroecological farming or chinampas without human activities). Instead, we found that the water in those canals exceeded the recommendations for pH values (>9), total coliforms (>240 CFU/ 100 mL), conductivity (>2000 μS/cm), and dissolved oxygen concentrations (<6.5 mg/L). However, nutrient concentrations were low. The structure of the canals near agroecological farming areas are narrow, shallow, and have low water flow, so alterations in the depth and width of these canals might result in improved water quality. The only sampling site that met most of the international and national guidelines for irrigation use was located in an area with many abandoned chinampas. Volunteers that participated in this study gained insights regarding the importance of being aware of anthropogenic impacts on ecosystems like the Xochimilco wetland, a place that is important to preserve because of its agricultural, ecological, and cultural significance.
Two exotic fishes, common carp (Cyprinus carpio) and tilapia (Oreochromis niloticus), were introduced more than 20 years ago into Xochimilco for aquaculture, and now dominate the system in terms of ...biomass and numbers. Over this same period, wild populations of the microendemic axolotl salamander (Ambystoma mexicanum) have been dramatically reduced, and it currently persists in isolated areas of this aquatic system, which is situated at the edge of Mexico City. In this study, we examine potential trophic interactions and niche overlap among two exotic fishes: carp and tilapia, and the native axolotl. Axolotl had more diverse diets and a higher trophic position compared to the exotics. Stable isotope analysis revealed substantial trophic niche overlap among axolotl and the exotics. The two exotics occupied a larger niche area than the axolotl, suggesting higher levels of omnivory and diet specialization. Current exotic fish removal efforts will further our understanding of interactions between the axolotl and exotic species, and are expected to benefit axolotl recovery efforts.
Native populations of the axolotl (
Ambystoma mexicanum), a microendemic salamander from Central Mexico, have seen alarming decline in the last decades owing to habitat loss caused by urban growth. ...The last remnant of its distribution is in a highly heterogeneous urban–rural water system in the Xochimilco region, at the southern edge of Mexico City. We developed a model of the species local distribution based on its ecological niche, using occurrence data and
ad hoc limnetic variables via the Genetic Algorithm for Rule-set Production (GARP), to identify suitable areas for the species and prioritize conservation efforts. Results indicated that potential distribution of the axolotl in Xochimilco is limited to 11 sites in six reduced, isolated, and scattered areas, located mostly in zones where traditional agriculture (
chinampas) is the primary land use. Recent surveys found only a single organism in the whole study region, in one of the predicted sites, suggesting a critical situation for the long-term survival of the axolotl in the wild, and demanding urgent actions toward habitat and population restoration. This study also illustrates the utility of niche modeling approaches for aquatic systems at a fine scale.
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