Background
Throughout history, human beings have tended to agglomerate along the margins of watercourses, where they have access to important resources, such as water, food, and raw materials [
1]. These areas tend to be naturally more fertile, favoring agriculture and ultimately contributing to their anthropogenization [
1]. In the present day, hydrological resources are exploited in a number of different ways, ranging from domestic, agricultural, and industrial consumption, through the removal and dilution of effluents and solid waste, to the generation of electricity [
2].
The initial consequence of the human occupation of river margins is deforestation, due to the demands for physical space [
3]. This results in soil exposure, leading to erosion, excessive leaching of nutrients, and the eventual siltation [
3]. The development of urban environments leads to an increase of nutrients concentration and fecal coliforms due to the discharge of domestic effluents [
4]. This contamination promotes modifications in the physical-chemical characteristics of the water, and in turn, the quality of the aquatic environment [
5]. The addition of nutrients promotes ecosystem-level problems, such as algal blooms, biochemical oxygen demand increase and hypoxia [
6]. Fecal contamination also contributes to hypoxia, as well as human illnesses [
6].
The contamination of water bodies impedes the exploitation of their resources by the population, in particular by reducing supplies for domestic consumption and usage [
7]. The degradation of aquatic ecosystems may also result in a decline in fishery stocks [
8], which may affect the economic income of some riverine communities. In addition to provide water and economic resources, aquatic ecosystems providing other ecosystem services that are less recognized by the society, such as cultural identity, spiritual and religious values, recreational activities, among others, that contribute to quality of life of human populations [
9]. Local people know, perceive and use the resources along their history with the environment where they live, therefore they are also responsible for the environmental changes occurring around them [
10] This relationship leads to a knowledge accumulation about the environmental changes and processes [
11]. Accessing perceptions of the local population makes it possible to identify these changes and their causes [
12,
13]. Therefore, Hanazaki et al. [
14] highlight the importance of including the perception of local human populations in obtaining information to help clarifying questions about the environmental changes occurring. These environmental changes and their relationship with the human societies have been better understood through approaches of historical ecology, which seeks to understand the conformation of contemporary and past cultures and landscapes [
15].
The understanding of the relationship between man and nature, as well as the anthropogenization of the environment, has been advancing in recent years through the adoption of interdisciplinary approaches, which combine different methods and theoretical perspectives to provide integrated insights into these phenomena (e. g. [
16,
17]). In this context, the present study integrated data on environmental data related to fecal coliform and trophic state index (TSI), Geographic Information System (GIS) analyses, and local knowledge provided by the resident population, with the objective of understanding the degradation of an urban river in northeastern Brazil over the past three decades, and in particular the consequences of this process for the river, its ichthyofauna, and the local riverside community.
Discussion
Urbanization is a multidimensional global process linked to the ongoing growth in human population and alterations in land use, a rapid and dynamics process, which may be difficult to predict [
29]. The urban growth in the studied site was evident through the GIS analysis and the local perception. However, despite the complementarity and concordance of these data, the urban expansion of community Beira Rio that occurred in the late twentieth century was most evident from local perception. This local perception was possibly influenced by urban growth that also occurred in community surroundings, since according to Fernandes et al. [
30] one’s perception is based on the entire visual environment surrounding him or her.
Urban expansion results in an increase in the production of waste, which is often disposed directly onto the ground or into bodies of water [
31], as observed in the present study, given the lack of basic public sanitation in the community, with effluents being discharged directly into the Capibaribe. The highest levels of fecal coliforms recorded in the present study corresponds to 160 times the maximum value permitted under Brazilian federal legislation [
22], reflecting the enormous quantities of domestic effluents being discharged into the river. Due to the synergistic and cumulative effects of river pollution (eg. [
32,
33]) these high contamination levels recorded possibly resulted from the discharge of domestic effluents by several urban centers upstream of the Beira Rio community. However, CPRH sampling station is located next to the Beira Rio community, so the recorded levels of fecal contamination possibly have higher contribution from waste dumped by the community.
The lack of basic sanitation and the inadequate disposal of urban waste are recurring problems in developing countries, where the scarcity of financial and technical resources limits the potential for the satisfactory processing and disposal of the residues produced by the urban population [
34]. The peripheral and unplanned growth of most Brazilian cities, together with the lack of basic infrastructure, have contributed to the present scenario, in which only half of the country’s municipalities has public sanitation systems, and even where they do exist, most of the effluents receive inadequate treatment before being discharged into bodies of water [
21]. According to local informants in the present study, there is a constant risk of schistosomiasis from contact with the river water, as confirmed by the high rates of contamination documented in the records available for the town of São Lourenço da Mata [
35]. The establishment of endemic diseases, such as schistosomiasis, is related to a complex of biological, social, political, and cultural factors, which are expressed in the living conditions of the local population [
36]. This reinforces the need for basic sanitation, not only for the recuperation of the environment, but also to guarantee public health.
Any ecosystem will have a natural capacity of resisting to degradation, stabilizing or assimilating the substances found in urban effluents, and maintaining the quality of the environment [
37], although the capacity for depuration of aquatic ecosystems may soon fall behind the increasing demands of urban development [
38]. In the present case, while the informants referred to the degradation of the river only by the end of the 1990s, it seems likely that the gradual accumulation of waste over the preceding years eventually exceeded the depuration capacity of the river by the late 1990s. According to the available data, fecal contamination of the river already exceeded legal limits at the beginning of the 1990s, although a peak in values was recorded between 1996 and 2000, corresponding approximately to the period of greatest environmental disturbance indicated by the informants. In addition, the river is suffering an ongoing process of eutrophization which, according to CETESB [
39] may have a series of negative consequences for the river and its resources, including increased fish mortality, an increase in algal biomass, and blooms of cyanobacteria. The eutrophization of bodies of water is a recurring problem in urbanized environments, especially densely-populated areas with an intense discharge of nutrients, as observed in China by Gao and Zhang [
40].
The loss of water quality affects the supply of ecosystem services to human populations, given that these services depend on the physical,chemical and biological conditions of the ecosystem [
9]. The bacteriological conditions of the Capibaribe recorded in the present study are consistent with the prohibition of all activities except navigation and landscape harmony, according to Brazilian legislation [
22].
The emphasis on ecosystem services reinforces the understanding of the relationship between the local population and the environment, in terms of its dependence on natural resources [
41]. The present study demonstrated that the degradation of the aquatic environment resulted in a loss of environmental services, modifying the habits of the local population, and their feelings in relation to the river. During the early years of the community, the residents had positive feelings toward the river, which they used for domestic supplies, drinking water, fishing, and recreational activities, whereas at the present time, the river has a negative image, being considered unpleasant and useless. The negative modifications of the river are related primarily to the color and odor of the water, as observed by Johnson et al. [
42] in an urban river basin, where the changes in the quality of the aquatic ecosystem were perceived by local residents primarily through their visual or olfactory perceptions. Additional changes perceived by the local population in this study were in the sediment and fish population. The accumulation of fine sediments and alterations of the natural riverbed are recurring problems in urbanized systems [
43].
The pollution of bodies of water may render fishing unviable due to the loss of species [
8] and the reduction in the quality of fishes [
44]. These factors were cited among the reasons for abandoning of fishery activities in the study area. The loss of fish species is a common problem in degraded environments [
45]. Despite the importance of the Capibaribe River to the state of Pernambuco, there are no previous studies that provide information on the diversity of its ichthyofauna, being the results of this research the only source available to understand the local fish fauna.
Fish are no longer considered to be a source of food by the informants from the Beira Rio community, due to the contamination of the water. A number of studies have shown that the fishes can become contaminated by the discharge of pollutants into aquatic ecosystems [
46]. Given the potential risks to human health and wellbeing, many populations that once depended primarily on fishery resources for their diet have abandoned this practice altogether [
47].
Exotic species may be introduced by man either intentionally or accidentally [
48]. The restocking of freshwater systems has been promoted by the Brazilian government as a strategy to guarantee the survival of artisanal fishermen by providing a source of income and employment [
49]. During the 1990s, thousands of fingerlings were released into ponds and reservoirs in Pernambuco, resulting in the dispersal of species such as curimatã (
Prochilodus sp.), tambaqui (
Colossoma macropomum), tilapia (
Oreochromis sp.), carp (
Cyprinus carpio, Hypophthalmichtys molitrix or
Aristichthys nobilis), and piau (
Leporinus sp.) [
49]. Some of these species were reported being found in the Beira Rio community during this same decade, except for the piau (
L. piau), which appeared only two or three years ago, following a flood. The arrival of
L. piau may have resulted from the accidental connection of the main channel of the river to fish farms or reservoirs located within the area flooded by the river. Fish farming is a common practice in many parts of Brazil, although the government agencies responsible for the monitoring of this activity do not control the dispersal of species, and lack environmental management requirements [
50].
Exotic fish species may cause ecological damage in new habitats, generally through an increase in competitive and predation pressures [
51].
Leporinus piau represents a threat to the other fish species due to its generalist habits and voracious appetite [
52], which enhance its potential competitiveness in comparison with the resident species. Despite this situation, informants considered positively the presence of
L. piau, due to the quality of its flesh.
Conclusions
The degradation of an urban river had negative effects on the river and its ichthyofauna, affecting the subsistence and intimate relationship of the adjacent human community with this environment. Despite the current degraded condition of the river, the local community still harbors hope that this river will someday become a pleasant environment for the local community, as long as the factors causing the degradation of the environment are corrected, in particular by building a public sanitation system, which would reduce the discharge of domestic effluents directly into the river. In general, however, no real expectation was found of a return to a fishery-based economy, especially as the locals have already adopted other means of subsistence. The current situation on this river emphasizes the urgent need for the establishment of mitigating measures in order to avoid its complete degradation. These measures will require efforts on social, cultural, and political fronts for the development of programs that contribute to the improvement of the quality of both the environment and the lives of local residents. In particular, there is a clear need for public works of infrastructure, in particular a sanitation system, combined with efforts to modify the consciousness of the community with regard to the need to avoid the discharge of waste into the river, and encourage the participation of local residents in recuperation and conservation projects. The integrated approach used in this study demonstrated the complementarity of the obtained data, which provided an understanding of the degradation process of an urban river, revealing the effectiveness of implementation of this approach.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
CAC conceived of the study. CAC, MSAN, GMAA and RES- Data collection literature survey and writing of the manuscript. JSM, CAC and MSAN participated in the analyses and interpretation of the ethnobiological data. THO and GMAA carried out the geoprocessing analyses. WS and ACAE supervised all research and participated in the taxonomic identification of fishes. All authors read and approved the final manuscript.
CAC and MSAN have research about ethnobiology, ecology and conservation. GMAA develops field research on landscape ecology and ethnoecology, and remote sensing applied to ecology. RES has research about fish ecology and conservation with emphasis on reproductive biology and environmental impacts. THO research’s about Remote Sensing, Geoprocessing and environment. JSM is a Professor at the State University of Paraíba and his research is centered in Local Ecological Knowledge of fishermen, crab gatherers and shellfish gatherers. WS and ACAE are Professors at the Federal Rural University of Pernambuco and research about taxonomy, biology and ecology of freshwater fish.