Functional groups can respond to changes in living environment and have a certain impact on ecosystem functions [19]. The difference of abundance is the result of habitat filtering, that is, the rank character with higher abundance can be considered as the character with better adaptability to regional environment [20]. Ecosystem function is essentially dependent on the functional group of the species, and which has become a powerful and reliable method to study the dynamic change of community by functional characters [21–23]. The large difference in spatial pattern of functional groups is the response to environmental changes and the tradeoff between different functions
Globally, changes in land use, especially loss of riparian forests, can lead to a reduction or change in the structure, function and diversity of macroinvertebrates in some river basin [24–26]. Once the riparian zone lacks the shelter of riverside forest, the sun will direct to the water surface and cause the water temperature to rise. Because the water temperature is close to the heat-resistant limit in tropical areas, some species of macroinvertebrates adapted to cold water cannot survive [27, 28]. Moreover, the decrease of leaf litter is the main food source of shredders, which will block the growth and development of group SH and make the aquatic ecosystem unbalanced, and ultimately affect the structure and function of the ecosystem [7]. Serious soil erosion in Muling River Basin, soil and water loss in riparian zones causes large amounts of sediment to enter rivers. The surface of river sediment is covered by muddy soil, which affects the growth of algae [4, 29]. At the same time, these sediments will also adhere to the surface of the body, trachea, and gill of the benthic animals, which leading to the disappearance of macroinvertebrates [30].
In this study, we demonstrated the impacts of environmental variables on benthic macroinvertebrates feeding functional groups. No significant differences in the FFGs were observed along season gradient, except group SC (Table 1). Mollusk (group SC) dominated at sampling sites of S25 ~ S28 in the downstream of river, which close to floodplain wetlands along Ussuri River. Guan et al. (2017) sampled macroinvertebrate assemblages along Wusuli River (upstream, midstream, and downstream), and agreed with the emerging theory suggesting that aquatic invertebrate assemblages in floodplain wetlands should change longitudinally along a river’s length and be affected by lateral connectivity of floodplain habitats with main river channels [31]. Wu et al. (2017) found that snails could be possess several attributes that should make them useful as potential environmental indicators in Sanjiang Plain, and the certain snail species may provide a robust and rapid indicator of environmental impacts in freshwater in Heilongjiang Province of China [32]. Next year, Guan et al. (2018) also confirmed that the snails (Mollusca: Gastropoda) can rapid assessments of wetland condition using aquatic invertebrates simple effective in northeastern China [33].
Macroinvertebrate community structure is usually determined by the physical structure and complexity of the habitat [34]. Aquatic vascular plants plays an important role in structuring macroinvertebrate species and selecting species related to functional groups dynamics and feeding habits [35, 36]. The distribution of macroinvertebrate is also determined by vegetation type, especially the structure and growth form of aquatic vascular plants [34]. Aquatic vascular plants affect the underwater climate and chemical properties by absorbing and releasing chemical substances (such as nutrients and antagonistic substances) [37]. However, as the growth of aquatic vascular plants in northern China is mainly affected by seasonal temperature changes, dominant communities can only be formed in summer and autumn [7].
In spring, the farmland near the Muling River basin contains a lot of nutrients (nitrogen and phosphorus) in the sediment of pesticide and chemical fertilizers. Chen et al. (2019) studies have shown that nitrogen can enter the water body through fish secretion and excretion [38]. Nitrogen-containing nutrients in the water body are absorbed by algae growth and carried down together through surface runoff to provide sufficient nutrients for the growth of plankton. Meanwhile, greatly increased the number of plankton which as the source of food for macroinvertebrates, such as group SH positively correlated with TN (Table 2).
Moreover, iron, as an element affecting chlorophyll synthesis in plants, is also a trace element needed for phytoplankton growth [39]. Trace element copper is an indispensable metal element for the metabolism of microelements and plants in cell membranes, which can affect the growth of plankton [40]. We guessing that heavy metal ion may contribute to primary productivity and indirectly affects secondary productivity by food chains in the aquatic ecosystems. Besides, hydrology is considered the paramount environmental control of freshwater wetlands, with temporary drying being a major constraint on aquatic insects [31–33, 41]. The movement group [7] of macroinvertebrates could be considered as a new method for monitoring and evaluating water quality in Muling River basin for further studies in the future.
