Natural and anthropogenic factors are responsible for changes in wetland function and structure. This research deals with the complexity of interactions among flood attributes, climatic data and land use trajectories to track the impact of land use changes for wetland management, over 30 years (1984- 2014). This paper presents a multi-temporal analysis of a floodplain to know the inter-annual ecohydrological variability, including extraordinary events of floods and droughts, using indicators of hydrological regime. It also presents a quantitative description of the geospatial variability in the Mogi Gua çu wetland components to assess the changes in the conversion, replacement, of wetland landscapes by anthropic growth activities. Flood attributes and anthropogenic pressures have altered temporal habitat variability in changes on the river course, in sandbars extent, and oxbow lake genesis and extinction, with a decline in the biota dependent on these habitats. These results have significant implications of the quick expansion of anthropogenic activities and provide key information about the impact of land use changes on the wetland function and structure. It is an objective tool to help the environmental management of wetland areas.
The Ramsar Convention’s definition of wetland is broad and, along with natural wetlands, encompasses human-made wetlands [
Natural and anthropogenic factors, as well as their synergistic combinations are mainly responsible for changes in wetland functions and structures [
Land use intensification is a major driver of naturalness and biodiversity loss, as well as reductions in local species diversity and biotic homogenization, which is a matter of great concern for conservation [
Land use changes in wetlands have altered temporal habitat variability in geomorphic templates (i.e. changes on the river course, in sandbar extent formation, and oxbow lake genesis and extinction) [
In tropical to subtropical regions, the predictability of flood pulse systems facilitates the evolutionary adaptation of organisms to spatiotemporal dynamics. The flood-pulsing systems in most of the South American wetlands oscillate between a terrestrial and an aquatic transition because precipitation regimes have marked rainy and dry seasons throughout the year. They provide a variety of ecosystem services, i.e. decomposition, regulating biogeochemical cycles, providing habitats, primary and secondary productivity and sustaining cultural practices [
Mogi-Guaçu wetland (Southern Brazil) may be considered a flood-pulsing system with significant hydrographic and physiographic modifications. The magnitude and intensity of flood pulse occurrence during the year did not reached the wetland full extent, resulting in the genesis and extinction of oxbow lakes at time intervals over the 30-year (1984-2014) [
This research deals with the complexity of interactions between flood attributes, climatic data, and different land use/cover, their temporal and spatial changes, over 30 years (1984-2014), to track the impact of land use/cover changes for improve wetland sustainable management.
The study was carried out in a wetland area located in a meander zone of the Mogi Guaçu River basin, subject to periodic flooding via overflow from the river channel [
The Mogi Guaçu River basin has three distinct geomorphological regions: the source area, which is characterized by steep slopes at a mean elevation of 1,650 m, located in the Bom Repouso Municipality (Minas Gerais State) on the Cristalino Plateau; the middle stretch river, which is characterized by a geological fault occupied by a meander zone and located in the northeastern region of São Paulo State on the Central Plateau; and the downstream stretch, where the river runs without meanders until it joins the Pardo River in the Pontal Municipality (São Paulo State at an elevation of 490 m [
The wetland study area occupies an area of 176.27 km². It generally features unconsolidated hydromorphic soils (certain reaches feature consolidated soils). The climate region (Köppen) is Aw type that characterizes a tropical climate with dry winters (May to October) and a rainy season (November to April). The minimum temperature is between 18.5˚C to 19˚C; the maximum temperature is 23.5˚C to 24˚C. The annual precipitation is 1100 to 1700 mm. The primary economic activity in the Mogi Guaçu River basin is related to sugarcane and orange cultivation, forestry and pastures.
The historical series of daily water level data is available at the São Paulo Basic Hydrologic Network [
the vegan package of R software [
Hydrological data and flood attributes were processed according to [
Wetland land use/cover dynamics were identified over the 30-year (1984-2014). The qualitative and quantitative land use/cover typologies were obtained through on-screen digitizing of Landsat-5 TM images (path 220, row 075; dated June 20, 1984; July 4, 1989; June 16, 1994; August 1, 1999; June 27, 2004; and August 12, 2009) and Landsat-8 OLI imagery (path 220, row 075; August 3, 2014) with multispectral composite of the near infrared, red and green bands using ArcGIS 10.2 software. All of the images were clear and nearly free of clouds. The classification accuracy to 2014 data was based on field data and determined using the Kappa (k) index [
Through quantitative land use/cover dynamics, over the 30-year (1984-2014), a land use change matrix for each five-year period between 1984 and 2014 was carried out using the raster [
Based on land use change matrix, pointing out the main types of gains and losses in each land use/cover category, four conversion contribution rates were calculated: Conversion-in (Cin), Conversion-out (Cout), Retention rate (R), and Area change rate (CR). The Cin is the ratio of the conversion area from other landscape elements to a specific landscape element to the total landscape conversion area; Cout is the ratio of the conversion area from a specific landscape element to another landscape; (R) is the retention rate of landscape type between the comparison time periods and shows the stability of landscape type; and CR is the level of landscape change in response to the landscape tendency [
Many biogeochemical processes in wetlands are closely related to the alternation of drought and flood periods, i.e. the frequency, intensity, duration and seasonality of connectivity between the wetland and the fluvial course [
Studies in the Mogi Guaçu wetland have shown that the bankfull discharge or the flow rate, when the water level exactly fills the river channel, is 380 m³/s in the Mogi Guaçu River. Above 380 m³/s, water overflows into the wetland. When the river reaches a flow rate of 752 m³/s, the total wetland area is flooded [
The flood attributes and climatic data in the Mogi Guaçu wetland over a 43-year (1971-2014) was used to infer which pulse attributes (e.g. frequency, intensity, tension, regularity, amplitude, seasonality) produce changes in community integration, phenological characteristics or determined population growth and to obtain synthetic indicators of the relationships between plants and the environment in which they live [
The flood pulses occur in the rainy season from November to April of each year. Hydrological data from 1971 to 2014 concerning the Mogi Guaçu wetland indicate that the average recurrence of floods (typical alternation of flood and drought phases) was 3.23 times/year, permanency = 29.12 days/year and FCQ = 0.087. The low FCQ values over the 43-year period (1971-2014) were used to compare partial periods within a time series to look for changes in the communities as a consequence of anthropogenic modifications in the hydrological regime of rivers.
Higher values of flood attributes, mainly river flow (maximum and average), flood pulse (maximum and average), potamophase, frequency, permanency and FCQ were observed from 1980-1984, 1990-1994 and 1995-1999 over the 43-year period (1971-2014), corresponding to the El Niño Southern Oscillation (ENSO) strong influence, especially for the warm ENSO-phase that causes large-scale precipitation anomalies in the Southeast.
The ENSO influences water-level fluctuations and discharge in the catchments of many tropical rivers [
In the wetland study area over the 43-year (1971-2014), the warm ENSO-phase would be narrowly confined just in 14 years, previously reported by [
Higher precipitation and river flood rates in the Mogi Guaçu wetland, with river flood values above 752 m³/s, may be related to up to two years of a warm El Niño phase occurrence. However, there is little evidence showing decreased precipitation in wetland areas over the last decade, but temperatures (mean and maximum) have increased 1˚C since 1971. Although the precipitation is strongly correlated with the flow rates (r = 0.69, p = 0.001), climate conditions are not a single factor to explain flood pulse magnitudes and flow rates.
Wetlands on sand soils recharge groundwater when flooded and are fed by groundwater in droughts, ensuring the flow river perennity. The water movement between the wetland and the ground may change according to hydrological conditions [
The gradual increase in temperature and low precipitation rates over the last decade has changed the natural dynamic and the minimum groundwater reserve to vegetation absorption with a decrease in the flow river rate in the long-term. Hidrological periodicity of the river flow and flood pulse. Natural processes changed the timing and magnitude of soil moisture and groundwater deficits by up to several years and caused the amplification of rainfall declines to be greater than in normal dry years [
Flow rates and flood pulse magnitudes observed since 2000 in the Mogi Guaçu wetland have not been sufficient to cover the entire wetland and have failed to reach 752 m³/s. They have also resulted in fluvial geomorphological processes, such as the extinction and genesis of oxbow lakes and changes of the river course, all of which have been accelerated by anthropogenic activities [
Three primary land use classes were identified for the study area (
Land use/cover typologies | Area (%) | |||||||
---|---|---|---|---|---|---|---|---|
Primary class | Secondary class | 1984 | 1989 | 1994 | 1999 | 2004 | 2009 | 2014 |
Aquatic | River | 4.64 | 4.11 | 4.19 | 4.28 | 4.37 | 4.39 | 3.10 |
Oxbow lake | 2.92 | 2.01 | 2.13 | 1.49 | 0.81 | 0.56 | 0.68 | |
Natural | Sandbars | 0.40 | 0.53 | 0.43 | 0.51 | 0.55 | 0.19 | 0.98 |
Marsh | 26.30 | 29.07 | 29.91 | 26.96 | 23.16 | 23.87 | 18.06 | |
Terrestrial Vegetation | 44.67 | 40.18 | 37.88 | 42.53 | 44.62 | 45.55 | 43.75 | |
Anthropogenic | Agriculture and exposure soil | 20.80 | 20.91 | 21.09 | 18.84 | 18.55 | 16.63 | 24.52 |
Urban area | 0.10 | 2.47 | 3.53 | 3.80 | 6.37 | 7.11 | 6.96 | |
Mining | 0.18 | 0.72 | 0.82 | 1.60 | 1.57 | 1.70 | 1.94 | |
Total | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 |
The four conversion rate values (CR, R Cin, and Cout) for the Mogi Guaçu wetland (
The natural land use/cover (sandbars, marsh, and terrestrial vegetation) was the prevalent land use, occupying above 63% of the total study area, and a range above 40% predominantly occupied by terrestrial vegetation land cover, over the 30-year period (
The changes in terrestrial vegetation area (
Years | 1984-1989 | 1989-1994 | 1994-1999 | 1999-2004 | 2004-2009 | 2009-2014 | |
---|---|---|---|---|---|---|---|
CR | 25.98 | 24.06 | 29.15 | 19.43 | 15.85 | 35.18 | |
Oxbow lake | R | 0.33 | 0.29 | 0.19 | 0.34 | 0.46 | 0.01 |
Cin | 0.04 | 0.06 | 0.04 | 0.02 | 0.01 | 0.02 | |
Cout | 0.08 | 0.06 | 0.06 | 0.05 | 0.03 | 0.02 | |
Sandbars | R | 0.32 | 0.21 | 0.2 | 0 | 0.18 | 0.16 |
Cin | 0.02 | 0.01 | 0.01 | 0.03 | 0.01 | 0.03 | |
Cout | 0.01 | 0.02 | 0.01 | 0.01 | 0.03 | 0.01 | |
Marsh | R | 0.76 | 0.74 | 0.62 | 0.72 | 0.8 | 0.5 |
Cin | 0.35 | 0.35 | 0.29 | 0.19 | 0.34 | 0.22 | |
Cout | 0.25 | 0.02 | 0.39 | 0.39 | 0.3 | 0.42 | |
Terrestrial vegetation | R | 0.79 | 0.78 | 0.84 | 0.92 | 0.89 | 0.78 |
Cin | 0.19 | 0.26 | 0.36 | 0.28 | 0.38 | 0.29 | |
Cout | 0.36 | 0.36 | 0.2 | 0.18 | 0.32 | 0.36 | |
Agriculture | R | 0.72 | 0.83 | 0.71 | 0.78 | 0.81 | 0.94 |
Cin | 0.23 | 0.15 | 0.13 | 0.19 | 0.1 | 0.31 | |
Cout | 0.23 | 0.15 | 0.21 | 0.21 | 0.22 | 0.04 | |
Urban | R | 1 | 0.87 | 0.78 | 0.73 | 0.96 | 0.96 |
Cin | 0.09 | 0.06 | 0.04 | 0.18 | 0.06 | 0 | |
Cout | 0 | 0.01 | 0.03 | 0.05 | 0.02 | 0.01 | |
Mining | R | 0.21 | 0.81 | 0.71 | 0.44 | 0.81 | 0.65 |
Cin | 0.03 | 0.01 | 0.03 | 0.04 | 0.03 | 0.03 | |
Cout | 0.01 | 0.01 | 0.01 | 0.05 | 0.02 | 0.02 | |
River | R | 0.57 | 0.53 | 0.38 | 0.75 | 0.73 | 0.18 |
Cin | 0.06 | 0.08 | 0.09 | 0.06 | 0.08 | 0.08 | |
Cout | 0.08 | 0.08 | 0.09 | 0.06 | 0.07 | 0.13 |
values (R > 0.78) emphasize a continuous replacement of terrestrial vegetation, with Cin lower than Cout during 1984-1989 (Cin = 0.19, Cout = 0.36), 1989-1994 (Cin = 0.26, Cout = 0.36), and 2009-2014 (Cin = 0.29, Cout = 0.36). Likewise, Cin is higher than the Cout during 1994-1999 (Cin = 0.36, Cout = 0.20), 1999-2004 (Cin = 0.28, Cout = 0.18) and 2004-2009 (Cin = 0.38, Cout = 0.32) (
The marsh//herbaceous was a dynamic land cover occupying around 18.0% - 30.0% of the total study area (
Although low retention rate values (R < 0.32) was observed for sandbars (
The aquatic land use (river channel and oxbow lakes) and others natural land cover (marsh) have gradually decreased (
The trajectory of oxbow lake and river land cover areas are a result of a continuous change in the temporal variability of the river channel (i.e. changes in the river course, genesis (II), and extinction (III) of oxbow lakes) (Figures 2(a)-(g)). All these changes in the Mogi Guaçu wetland are quite fast due to intensive erosion and sedimentation resulting from human and urban occupation, development of new mining areas, and vegetation removal for sugarcane cultivation increasing [
The Cin and Cout rate values highlight the impact of land use/cover changes based on the conversion between a specific land use to another type which are highly dependent on the percentages of areas occupied in the wetland. Oxbow lakes, sandbars and river channel land cover occupied around 4.79% - 7.91% of total wetland area, with lower Cin and Cout rate values than other types of land use/cover, over the 30-year period (
The low Retention Rate (R < 0.50) values (
However, a decrease in the area of river channel land cover was observed more clearly from 2009 to 2014, corresponding to a minimum R value (0.18), with Cin (0.08) lower than Cout value (0.13) (
These processes have occurred naturally in the wetlands over centuries as a result of climate conditions and flood attributes that explain flood pulse magnitudes and flow rates, particularly, influenced by rainfall irregularity in the rainy season. However they can be accelerated by intensive agriculture activity similar to that observed for the Mogi Guaçu floodplain river [
The anthropogenic land use/cover intensification threatens biodiversity by reducing the α-diversity of many taxa, particularly due oxbow lake extinction, over the 30 years period. Similarly, β-diversity between oxbow lake and marsh land cover may decrease due to loss of these habitats through terrestrial vegetation retention rates, over the 30-year period (
Terrestrial vegetation and agriculture and bare soil land use/cover showed high R values, ranging from 0.71 to 1.00 (
Furthermore, agriculture and bare soil showed high R values, ranging from 0.71 to 0.94, characterized by prevalence and minimal changes for this land cover. The Cin and Cout rate values did not change from 1984 to 1994, corroborating this condition. The agriculture and bare soil land cover changes are highlighted from 1994 to 2009, when Cin was lower than the Cout rate values, except for the period from 2009 to 2014 when Cin was higher than the Cout value (
Urban and mining land cover have lower differences of Cin and Cout rate values (
Over the 30-year period, the main land use trajectories in the Mogi Guaçu wetland was anthropogenic occupation. Sugarcane cultivation, development of new mining areas and sand removal, riparian forest removal, overfishing, alcohol distilleries, as well as pulp and paper plants are the main pressure drivers on wetland biodiversity.
The transformation of natural vegetation into cropland and urban area is an increasingly recognized threat to many South American wetlands, being of particular interest because wetlands affected by these activities leave out capacity to provide ecosystem services [
The new Brazilian “Forest Code” has contributed to the agricultural expansion in wetlands, because the permanent protection zone of wetlands has been significantly reduced [
The Secretary of State for the Environment (São Paulo, Brazil) defined the Area Under Special Protection of Jataí (ASPE Jatai), by Resolution No. 92, September 21, 2013, due the anthropogenic pressure exerted on the all Mogi Gaçu River basin, and the importance of conservation of the most representative forest remnants, Luís Antônio Experimental Station and Jataí Ecological Station. The ASPE Jataí, with approximately 22,494 ha (
Therefore, implementing ecological and economic zoning on the Mogi Guaçu River basin is necessary to ensure the protection and conservation of water resources and ecological life-support systems, particularly in the surrounding municipalities. These zoning would require the maintenance of land use standards based on biotic, geological, agricultural, extractive and cultural characteristics, among others, and aim to improve the well-being of the local population. Environmental zoning throughout the Mogi Guaçu River basin can be subsidized and supported by Environmental Secretary Resolution No. 92/2013, which de
fines the ASPE Jatai because of local anthropogenic pressures, influencing in availability and quality of water resources and representative forest remnants, and balance socio-economic development with environmental conservation.
Specific regulations are essential for the ecological integrity maintenance for wetland management. Moreover, monitoring has become the focus of the Ramsar Convention [
Although rainfall is highly correlated with flow rates values, groundwater availability and land use changes are mainly driving forces that can affect hydrological periodicity of the river flow intensity and flood pulse magnitude. Higher values of all flood attributes were observed from 1980 to 1984, when the very strong warm El Niño Southern Oscillation phase occurred.
The main land use change occurred from 1994 to 1999 and 2009 to 2014. It was related to higher total landscape conversion rate values, and consequently, lower retention rate values for oxbow lakes, sandbars and rivers. The habitat diversity in wetland (oxbow lakes, sandbars and rivers) declined, while terrestrial vegetation and agricultural land cover increased, and these overall mosaics became more continuous and homogenous.
As terrestrial vegetation and agricultural expansion show an increase tendency scenario, over the 30-year period, the remaining natural habitats, as oxbow lakes, sandbars and marsh, have been modified to accommodate anthropogenic land cover. The extension, connectivity and shape complexity of Mogi Guaçu wetland result from the transition in land use/cover from natural to anthropogenic landscape. It means that wetland extension was dependent of their land use context, over the 30 years (1984-2014).
In the events of continuity of prolonged drought period, the irregularity of the hydrological period influencing the level of river flow, and the occurrence of periodic flooding pulses, we conclude the paper by considering the land use/cover trajectory, over the 30-year period, as the main driver for Mogi-Guaçu wetland to undergoing a quick transition from natural to cultural landscape. A more precise scenario points that Mogi-Guaçu wetland is currently threatened by a land use unsustainable trend related to a quick anthropic occupation of the floodplain river, resulting in loss of habitat, biodiversity and ecosystem services due to land use changes and its impact on the structure and function of wetlands. These changes are promoting unstable conditions within the Mogi Guaçu floodplain river and may soon approach a climax, beyond which the natural wetland ecosystem will be unable to sustain them.
These results make it possible for policy makers, scientists and stakeholders to identify at a glance the land uses which are hindered or enhanced under various scenarios of land use change, over the 30-year period, and makes it possible to explore the trade-offs between them to improve wetland management. This first effort to develop and apply rate values of land use conversion on land use/cover trajectory in a wetland ecosystem may find this methodology useful for monitoring and management others ecosystems with similar vulnerabilities and conservation issues.
Fushita, A.T. and Santos, J.E. (2017) Land Use Change Trajectories for Wetland Management (Mogi-Guaçu Floodplan River, Southern Brazil). Journal of Geoscience and Environment Protection, 5, 62-76. https://doi.org/10.4236/gep.2017.510006