Effect of Hydrological Connectivity on the Phosphorus Buffering Capacity of an Urban Floodplain

Abstract

Floodplains can perform nutrient buffering functions and therefore influence the riverine nutrient dynamics depending on the extent of the hydrological connectivity. This work focused on quantifying the adsorption/desorption potential of a degraded floodplain of the Danube River (Lower Lobau) based on sediment characterization (grain size distribution, organic content, and P-fractions) and sediment type-specific P-adsorption via batch experiments. We established an adsorption/desorption budget model with a high temporal and spatial resolution. With this model, we identified spatial patterns related to hydrology and calculated the phosphorus-buffering capacity of permanent and temporary floodplain water bodies. Sediment characteristics were defined by the distance to the inflow area and the hydrological connectivity of the floodplain water bodies. The main factor for the concentration of total phosphorus (P tot) in the sediments was the grain size distribution. P tot was 10 times higher in silt-dominated sediments compared with gravel-dominated sediments. Inorganic phosphorus (P inorg) ranged between 36 and 90%, depending on the organic content of the sediments. Both the adsorption and the desorption potential of soluble reactive phosphorus (SRP) were highest in large, frequently connected water bodies and were strongly controlled by hydrology. The total adsorption potential of the floodplain was up to 40 times higher in wet years (e.g., 2002) than in dry years (e.g., 2003), when floodplain water bodies were connected less frequently to the main channel of the Danube. Up to 75% of the adsorbed SRP was desorbed and released into the water column after periods of connection. Consequently, SRP adsorption directly reduced the P-load in the Danube River main channel. The adsorption/desorption mechanisms worked as a buffering system by taking up the SRP imported during floods and releasing it over a longer period after the floods. This stimulated high primary production in the floodplain water bodies and impacted the overall P-retention of the floodplain.

An Integrative Conceptualization of Floodplain Storage

“…Floodplains can also act as sources of dissolved organic matter and organic carbon to channels during high flows (e.g., Atkinson et al., 2019). On a degraded portion of the Danube River floodplain at Vienna, Austria, sediment grain size and hydrological connectivity of floodplain water bodies strongly influenced adsorption/desorption of phosphorus, with greater floodplain adsorption in fine sediments and during hydrologically connected, wet years (Preiner et al., 2020).…”

“…Fluctuating water levels on floodplains create aerobic and anaerobic conditions that enhance nitrification and denitrification in sediment (Groffman et al., 1988; Koschorreck & Darwich, 2003). Dissolved N concentrations and chemical form change as the water reacts with the surrounding matrix, especially in slower, subsurface flow, or as biotic communities such as microbes or algae take up some of the N compounds and biochemically transform them (e.g., Preiner et al., 2020; Wentz et al., 2014).…”

Landscape Preferences of Visitors to the Danube Floodplains National Park, Vienna

“…Whereas parts of the national park area are exposed to the high hydrological dynamics of the Danube River, the wetlands of the Lobau are subjected to limited hydrological dynamics, leading to heterogeneous floodplain areas. This results in ecological gradients related to nutrient dynamics [26,31] and aquatic vegetation [32], as well as a high diversity of habitats and plant and animal species in the national park [33,34]. Characteristic faunal elements are the European pond terrapin (Emys orbicularis), with the only autochthonous population in Austria occurring in the Danube Floodplains National Park [35], the little bittern (Ixobrychus minutus) [36], the European kingfisher (Alcedo atthis), a flagship species for natural dynamic riparian landscapes and floodplains [37], and the European beaver (Castor fiber) [38].…”

Effects of Two-Stage Ditch and Natural Floodplains on Sediment Processes Driven by Different Hydrological Conditions

“…Sedimentary SRP tends to equilibrate with stream water SRP during periods of low biological activity and is an important P source for sediment biofilms during high biological activity [44,61]. Thus, SRP concentrations in the sediments may change independently of sediment turnover and dependently on hydrology [62], making it a non-ideal parameter for monitoring restoration effects on sediment texture.…”