Contribution of nitrogen fixation to the external nitrogen load of a water quality control reservoir (Kis-Balaton Water Protection System, Hungary)

Abstract

To reduce external nutrient loading by the greatest nutrient transporter to Lake Balaton, the Kis-Balaton Water Protection System commenced operation in 1985. Cyanobacterial blooms (Cylindrospermopsis raciborskii, Aphanizomenon sp. and Anabaena sp.) cause nitrogen loading via nitrogen fixation, which can exceed the total external N-load to the reservoir during the summer. Nitrogen fixation of phytoplankton in the system in 2009 was measured using the 15 N-isotope technique. The light dependence of fixation was described by an exponential saturated curve which was then used to calculate daily nitrogen fixation. The total amount of nitrogen fixed during summer months (July-August) exceeded 170 tons for the 21 km 2 of open water area, which was more than three times higher than the external load by inflows. Total nitrogen: total phosphorus mass ratios (2.5−11.5) favoured the development of a N 2 -fixing cyanobacterial bloom, the contribution of which to the total algae biomass varied between 50 and 90%. The estimated primary production of phytoplankton was used to calculate the contribution of nitrogen fixation (0.01−28%) to algae nitrogen demand. Nitrogen fixing cyanobacteria were found to play a key role in addressing the nitrogen demand of phytoplankton.

The response of nitrogen fixing cyanobacteria to a reduction in nitrogen loading

“…Both the P concentrations and light intensities in our microcosms were higher than those typical during summer in Langer See (Supporting Information S2), and in addition to explaining the higher biovolumes and N 2 -fixation rates in the microcosms, they may also have improved the Nostocales ability to adapt to the N addition gradient. Nevertheless, the rates measured in our manipulated microcosms (1.8-13.3 μg N mm −3 d −1 ) were of the same magnitude as those observed under natural conditions (0.06-18.4 μg N mm −3 d −1 ) in the studies of Gu et al (1997) and Horváth, Mátyás, Süle, & Présing, 2013. We converted the published per litre rates of Gu et al (1997) and Horváth et al (2013) to rates per Nostocales biovolume using information extracted from Figure 4 (Gu, Havens, Schelske, & Rosen, 1997) and from Figure 2 and Table 2 ( Horváth et al, 2013), and assuming 12 hr of sufficient light for fixation per day.…”

Long‐term changes in the fish assemblage structure of a shallow eutrophic reservoir (Lake Hídvégi, Hungary), with special reference to the exotic Carassius gibelio

“…The escaped fish specimens were drifted downstream and were captured in the reservoir. Fish fauna composition of the latter years of the studied period showed strong relationship with the mean concentration of total dissolved solids, which normally indicates the ongoing eutrophication process (Hatvani et al, 2011;Horváth et al, 2013).…”

“…In this pioneer phase, decay of inundated organic matter was dominant among internal processes, as significant correlation with BOD and NH 4 þ shows. Fish fauna composition of the latter years of the studied period showed strong relationship with the mean concentration of total dissolved solids, which normally indicates the ongoing eutrophication process (Hatvani et al, 2011;Horváth et al, 2013). It might lead to the assumption that these parameters had only a minor influence on the composition of the fish assemblage.…”

Remote sensing of macrophyte morphological traits: Implications for the management of shallow lakes

“…We must point out that the nutrient stock in T. natans meadows is likely to be an underestimation of the real nutrient uptake because we only considered above-water biomass (e.g., in July above and below water biomass of Tn were 60% and 40% of total biomass; Pinardi et al, 2011) and without leaf turnover during the whole vegetative period (e.g., by doubling the maximum standing stock; galanti and Topa esposito, 1996). if we assume that these values are generally representative of the allocation of biomass above and below water, and an equal allocation of nutrients for above and below water plant parts, then we estimate that the total nutrient storage in T. natans biomass is up to 11.7 n t and 1.3 P t. according to published works describing nutrient or chemical inflow and water discharge data over time, we calculate a total load for the growing season period (May-october) of 72-206 t n and 6-13 t P (szilagyi et al, 1990;Pomogyi, 1993;Tátrai et al, 2000;hatvani et al, 2011;horváth et al, 2013;Paulovits et al, 2014). The comparison of nutrient content in macrophyte beds derived from aPeX maps with nutrient load inflowing by the Zala river evidenced that about 6-16% and 10-21% of n and P, respectively, can be temporarily stored in T. natans biomass.…”