Changes in composition of aquatic bird assemblages associated with changing in water levels in the Aquatic Terrestrial Transitional Zone of the Pantanal wetland Brazil Mudança na composição de assembleia de aves aquáticas associadas com mudanças no nível de água em uma Zona de Transição Terrestre Aquática no Pantanal de Mato Grosso, Brasil

The Pantanal wetland Mato Grosso, Brazil is among the largest floodplains in the world, with a mosaic of different habitats and rich aquatic and terrestrial biota. The habitat mosaics are found in the Chacororé and Sinhá Mariana lake System. These parental lakes of the Cuiabá River, a left tributary of the Upper Paraguay River, are known for their aquatic productivity and scenic beauty. The Research, Society and Development, v. 9, n. 10, e4479108555, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.8555 2 characteristics of these lakes and their floodplains are showed through the difference between their waters, the diversity of the aquatic macrophytes communities, fish communities and aquatic birds. Our study looked at changes in limnological variables as well as diversity of aquatic birds, during high water or flooded phase; medium water or receding phase; and the low water or dry phase. We used a temporary small lagoon in the floodplain of this system as our study area. The flood pulse is the main ecological factor affecting the Pantanal; it modifies ecological process and species composition. The water depth decreases during the season, decreasing electrical conductivity, dissolved phosphate and nitrate, water transparency, dissolved oxygen and biomass of aquatic macrophyte; and increasing calcium, total phosphorus and total nitrogen. We also observed increase in species richness and abundance of aquatic birds during the receding phase. Results show that the number of species (density) of aquatic birds increased from 10 to 30 species and the numbers of individuals from 40 to 936. The maximum richness and abundance of aquatic birds was registered during the receding phase.

characteristics of these lakes and their floodplains are showed through the difference between their waters, the diversity of the aquatic macrophytes communities, fish communities and aquatic birds. Our study looked at changes in limnological variables as well as diversity of aquatic birds, during high water or flooded phase; medium water or receding phase; and the low water or dry phase. We used a temporary small lagoon in the floodplain of this system as our study area. The flood pulse is the main ecological factor affecting the Pantanal; it modifies ecological process and species composition. The water depth decreases during the season, decreasing electrical conductivity, dissolved phosphate and nitrate, water transparency, dissolved oxygen and biomass of aquatic macrophyte; and increasing calcium, total phosphorus and total nitrogen. We also observed increase in species richness and abundance of aquatic birds during the receding phase. Results show that the number of species (density) of aquatic birds increased from 10 to 30 species and the numbers of individuals from 40 to 936. The maximum richness and abundance of aquatic birds was registered during the receding phase.

Introduction
The Brazilian Pantanal, is the largest floodplain in the world. It is a mosaic of different habitats with a rich aquatic and terrestrial biota. It is an inland delta, where many rivers converge on the main river channel, the Upper Paraguay River. Habitats within this landscape can be found in the Chacororé and Sinhá Mariana lake system. These parental lakes of the Cuiaba River, a tributary of the Upper Paraguay River, are known for their aquatic productivity and scenic beauty. The water characteristics of these lakes and their floodplains are demonstrated through the difference in their waters, the diversity of the aquatic macrophytes, fishes and aquatic birds' communities (Frota et al 2020;Ghosh;Biswas 2015;Schmidt-Mumm;Janauer 2014;Da Silva 2005).
Studies estimate 730 regional species, including migrants, accidentals visitors and introduced species, with 500 species in the Pantanal region alone, of these 500 species, about Development, v. 9, n. 10, e4479108555, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.8555 4 to know the behavior and ecology of these species are very important to think on conservation and management of the Pantanal species.
The objective of this study was to examine relationship between flood stage, water characteristics and avian assemblage diversity and species composition.

Metodology
This study was made using field research, by survey of bird abundance and species and water samples collects, that were analysed in laboratory for nutrient concentration. Is characterized as quali-quanti research (Pereira et al 2018).
A bird census was conducted during each hydrological period in order to obtain the number of the aquatic birds. During the high and receding phase, the census was conducted by boat around the lake during the early morning and in the afternoon. In the dry phase, observers walk around the dry lakes. All species observations around the edge of the lake were confirmed with binoculars (7x50mm) transects were defined with a GPS. The systematic ordination of the birds was done according to Sick (1997).
To the fields water samples were collected in the "lago dos Sonhos", the collects were realized during dry season (august) and during the raining season (March) and the receding phase was collected on may in the littoral region.
The Physical-Chemical variables of water were measured in field, the method are described in Nunes & Da Silva (2005) by using a set of specific equipment for the analyses of the water of the ATTZ: pHmeter 320 SET/WTW, Oximeter 196 WTW,conductivity,196 WTW, Mercury Bulb Thermometer, Termistor of the oximeter 196 WTW, rope with weight and band measure, Secchi disk, to measure the water transparency and depth Turbidimeter 2100 -HACH.
The particulate nitrogen was analyzed using methodology described from Anderson and Ingram, 1996. The ammonium ion, nitrate, total phosphorous and the orthophosphate were analyzed using methods from Carmouze (1994).

Study area
The Chacorore-Sinhá Mariana lake system is located between the 16º 14' and 16º 16' South and 55º 57' and 55º 58' West, in the basin of the Cuiaba river in the municipality of Santo Antonio de Leverger and Barão de Melgaço, Mato Grosso state. This lake system connects with Cuiabá Research, Society and Development, v. 9, n. 10, e4479108555, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.8555 River, through a complex network of channels locally called "corixos". The Chacororé lake is characterized by high available nutrients, conductivity, turbidity and low transparency of the water, while Sinhá Mariana lake is characterized by black water, low nutrients concentration, conductivity, turbidity and very high transparency Da Silva 2005) (Figure 1). The period of high water occurs between January and March and the receding phase April to June. During this time the water accumulates in the ATTZ (Aquatic Terrestrial Transition Zone), forming a small lake in a basin that we call "Lake of the Dreams" in the figure 1 we show where is located this sample site. Research, Society and Development, v. 9, n. 10, e4479108555, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.8555 6

Results and Discussion
The limnology of ATTZ depends on the connectivity with the lakes or rivers, the geology and the rate of decomposition of the aquatic macrophytes and terrestrial herbaceous plants grow up, respectively, during flooding and drying periods. The connectivity into the lake of the Dreams comes from the Sinhá Mariana Lake, through a decrease elevation. The difference on water level, between the low and high water periods, was 3m. Transparence Secchi followed the same patterns the water level, raising the higher water and decreasing as the water diminished. In the flood phase, just species, which dive for fish, can remain in the area, for example Phalacrocorax brasilianus. Anhinga anhinga, Sterna superciliaris e Megacerile torquata that uses the high transparency for foraging. intermediary, but interesting, because the species, which appears during this phase, hunting by passing the beak into the water and it, is not necessary an optimal vision focus.
The air and water temperature not showed a high variation during the three phases of research in this area (Figure 3). It seems not affect the presence or absence of the birds on the area. The range of variation of air temperature were between 22,5ºC on low water to 30ºC on receding phase. Water temperature variate from 21 ºC to 29ºC on receding phase.  Total phosphorous was 0.703 mg.L -1 in the low water and 0.453 mg.L -1 in the high water, during receding the concentration was 0,689 mg.L -1 dissolved phosphorous did not show any variation among hydrological cycles.
The table 1 and 2 shows the number of species on each hydrological periods, and  Shannon diversity was higher during receding phase and lower during the high water periods. In the receding phase, the number of individuals was four times higher on the low water period, 23 times higher than high water period. Receding and low water periods decrease water volume, concentration of fish populations improving foraging conditions for aquatic birds. Limnological conditions associated with, dissolved oxygen, water temperature and transparency, all of which improves the survival of a great concentration of fish. Those serve as basic food for aquatic birds.  Diversity was higher during receding (2,29) and low water (2,11) periods. The number of individuals was four times higher on the receding period and 23 times higher than high water period. Receding and low water periods decrease depth and water volume favoring fish concentration and adequate foraging conditions to aquatic birds. Receding water is the period that most favors abundance of aquatic birds due to limnological conditions such as water volume, depth, dissolved oxygen, water temperature and transparency, all of which guarantees the survival of a great concentration of fish. Those serve as basic food for aquatic birds. The highest numbers of birds were observed along the shoreline of the lake, most likely because these areas are shallow enough to allow the aquatic birds to walk and look for food, the same pattern was observed by Almeida et al ( Research, Society and Development, v. 9, n. 10, e4479108555, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.8555 depths of 1m or less attract a large density of aquatic birds, mainly herons, that prefer to forage in environment with shallow depth and without vegetation or grasses in the border areas. Egretta thula feeds in areas without or with very little river-side vegetation, and were rarely found in groups, with exception of areas with big concentrations of fish, Ardea cocoi feed in the same body of water that Ardea alba prefers, i.e. also in shallow water without vegetation (Willard 1985).
Many bird species forage using vision, making transparency and depth important determinants of foraging areas. According to Whingham et al. (2001), many aquatic bird species use the depth and the variation of the water level as parameter to delimitate the foraging area and/or breeding area.
The maintenance of this kind of habitat favors the life strategies of many aquatic birds, which depends on the quality of habitats defined by limnologicals variables, mainly depth, transparency, turbidity and dissolved oxygen. Willard (1985), showed that piscivorous species can be divided into four classes based on foraging bahavior: 1 -Swimming -American Anhinga and Olivaceous Cormorant, look for prey under water, demanding a high depth and transparency; 2wadingsuch as Tigrisoma spp, Ardea, Egretta, Butorides, which use habitats without vegetation and low depth.
The class 3 -Wait Perch -Kingfishers, which wait on a branch and then dive to capture identified prey, making availability of perches important, and 4icruisingcommon behavior to Pandion haeliaetus, which conducts aerial/visual hunts and therefore needs habitat with high transparency and low turbidity. Kushlan et al. (1988), showed that the differences in the length of foraging and the behavior linked to foraging of species hunting in the same place, worked so that Ardeidae and Alcedinidae avoided direct competition.

Conclusions
This study shows that the flood stage affects limnological conditions, concentration, and number of species and abundance of aquatic birds in the ATTZ of the lake system Chacororé-Sinhá Mariana. During shallow water, low and receding water periods, diversity and abundance of birds are high. Changes in the flood pulse that favors the extremes of water permanence or completely dryness may affect these variables and diminish the ecological and touristy value of the system. We consider importante the maintaence of this kind of research in the area, to understand the dinamyc of the waterfowla under the changes of the water level and the climate changes in the Pantanal region, the major understanding permiss us to plan the better way to protected this área.