Water management infrastructure alters plant species composition, functional diversity and soil condition in a livestock impaired mosaic of wetlands

Abstract

Wetlands are fundamental in conserving biodiversity, regulating pollution, and as natural reservoirs of water, among several other contributions to people. Wetlands not only harbor for a great number of animal species, but also a high diversity of plant communities (Moges et al., 2017; Raulings et al., 2010). Its extraordinary diversity sustains critical ecosystem functions, providing diverse ecological services and socio-economic benefits to locals (Mitsch et al., 2015). Wetlands are also threatened by many factors which difficult their conservation (e.g., over-exploitation, habitat fragmentation, water eutrophication and pollution, human alteration of natural water cycles and species invasion; Gardner et al., 2015). Most human interventions (livestock raising, crops, forestry and urbanizations) involve the implementation of water management infrastructure (Blanco and Méndez, 2010; Sica et al., 2016; Warner et al., 2018). Water management infrastructure decouples areas from its natural hydrological regime, decreasing water availability and altering vegetation growth dynamics, particularly in the context of disturbances or adverse hydro-climactic scenarios (Aquino et al., 2021a, 2021b; R. Foti et al., 2012; Warner et al., 2018; Wen et al., 2012). In wetlands, plant community development has been related to different components of the hydrological regime (Romano Foti et al., 2012; Marchetti and Aceñolaza, 2012, 2011; Morandeira and Kandus, 2015). Its variability exerts strong influence shaping ecosystem biodiversity. The flood pulse determines water availability for plant growth (Wen et al., 2012), and modifies sediment and soil nutrient dynamics (Baldwin and Mitchell, 2000; Primost et al., 2022). In this matter, hydromorphic soils comprise a key component of wetland ecosystems as its characteristics also determine an adequate substrate for root growth as well as conditions for water storage and availability (Keddy, 2016; Taboada and Alvarez, 2008). Degradation of hydromorphic soils as a consequence of productive activities usually causes drastic changes in the environment that imply consolidation, subsidence and compaction of the soil due to less waterlogging conditions (Evenson et al., 2018; Garnier et al., 2007). Soil degradation alters plant diversity and negatively affects wetland species growth, as the loss of hydromorphic soil promotes the invasion of terrestrial species(Zhang et al., 2019). In this context, grazing and trampling by domestic and wild herbivores constitutes one of the most prevalent disturbance agents (Magnano et al., 2019; Reeves and Champion, 2004). Its impact on plant communities and soil usually varies in space due to selective dietary choices (Marion et al., 2010; WallisDeVries et al., 1999). Grazing is also dependent on and affects plant morphological and functional traits (Díaz et al., 2007), which usually results in vegetation patchiness as well as disrupted cycling and storage of nutrients (Lavorel et al., 2011; McIntyre and Lavorel, 2001). However, low to intermediate grazing intensity promotes species diversity (Magnano et al., 2019; Marion et al., 2010; Reeves and Champion, 2004). For these reasons, changes in grazer identities and densities in response to climate and/or land use change are increasingly considered as an important element of global change (Gardner and Finlayson, 2018). Particularly in wetland ecosystems, grazing and trampling can promote shifts in plant species composition. Not only livestock, but also environmental constraints such as the hydrologic regime exert a remarkable effect on both structural and functional traits of wetland vegetation (Morandeira and Kandus, 2016), plant diversity and macrophyte distribution (Magnano et al., 2019; Moges et al., 2017; Morandeira and Kandus, 2015; Reeves and Champion, 2004). Thus, evaluating the effect of livestock grazing intensification becomes essential in the context of unrestricted and unregulated implementation of water management infrastructure, which is occurring in many wetlands under differing socio-ecological scenarios across the globe (Gardner and Finlayson, 2018). Due to a recent expansion of agriculture over grazing grasslands in Argentina (Aizen et al., 2009), agriculturally marginal areas such as the non-insular portion of the Lower Delta of the Paraná River (LDPR) shifted towards a much more intensive livestock production system (Quintana et al., 2014). Livestock intensification was accompanied by a widespread and unregulated implementation of water management infrastructure (Aquino et al., 2021a; Minotti, 2019), sowed pastures and fodder supplements (Quintana et al., 2014; Sica et al., 2016). Additionally, it was followed by the recent implementation of bubaline livestock farming (Bubalus bubalis), which allegedly can do without water management infrastructure and thus, is expected to exert a lower influence on wetlands’ condition. However, its effects on soil, structural and functional attributes of plant communities are unknown. Hence, the main novelty of this study is to analyze whether water management infrastructure affects not only the structure, but also the function of plant communities, as well as the quality and fertility of soils in a highly heterogeneous mosaic of livestock impaired wetlands. To that end, we determined the species composition and diversity of wetland plant communities across five livestock management practices (LMP), whose differences are mainly based on livestock type (bovine or bubaline), and whether water management infrastructure is implemented (polder, channelization, none) In the context of livestock raising intensification, the following research questions guided our analyses: Does water management infrastructure (1) alter plant species composition, (2) decrease the structural and functional diversity of plant communities or (3) reduce the quality and fertility of soils. Lastly, (4) does buffalo exert a differing effect on the aforementioned plant and soil attributes?