Carbon metabolism and nutrient balance in a hypereutrophic semi-intensive fishpond

Abstract

Eutrophication and nutrient pollution is a serious problem in many fish aquaculture ponds, whose causes are often not well documented. The efficiency of using inputs for fish production in a hypereutrophic fishpond (Dehtář), was evaluated using organic carbon (OC), nitrogen (N) and phosphorus (P) balances and measurement of ecosystem metabolism rates in 2015. Primary production and feeds were the main inputs of OC and contributed 82% and 13% to the total OC input, respectively. Feeds and manure were the major inputs of nutrients and contributed 73% and 86% of the total inputs of N and P, respectively. Ecosystem respiration, accumulation in water and accumulation in sediment were the main fates of OC, N and P, respectively. They accounted for 79%, 52% and 61% of OC, N and P inputs. The efficiency of using OC, N and P inputs to produce fish biomass was very low and represented 0.9%, 25% and 23% of total OC, N, and P inputs, indicating an excessive phytoplankton production and overdosing of fish feeds and manure. Dehtář pond was slightly autotrophic and phosphorus availability did not limit the phytoplankton growth. The low efficiency of using inputs was attributed to the low digestibility of raw cereals grain used as feed and the inability of planktonic food webs to transfer the primary production to fish due to high predatory pressure of fish stock on zooplankton. The primary production is an important input of OC in semi-intensive fishponds and should be considered in evaluations of fish production efficiency.

Seasonal Development of Phytoplankton in South Bohemian Fishponds (Czechia)

“…Hyphothesis H2. In line with a high fish predation scenario of the revised PEG model (Figure 2 in [33]), neither the spring peak of phytoplankton nor the clear-water phase were observed in the studied fishponds.…”

“…Studied hypertrophic and eutrophic fishponds (with a mean TP of 200 µg L −1 and 130 µg L −1 , respectively) were used for commercial fish farming. The high concentration of TP was caused by weekly auxiliary feeding by cereals, which added more than 50% of the overall nutrient supply to the pond ecosystem [32,33]. On the other hand, mesotrophic ponds, with a mean TP concentration of 40 µg L −1 , were used only for recreational fishing.…”

“…Nitrogen input from the watershed [33] was not denitrified during winter and early spring, resulting in high NO 3 -N concentration during spring (Supplementary Figure S2b). Rising temperatures in spring triggered the denitrification that effectively released N from fishponds, including that from auxiliary feed (Figure 7).…”

Spatial and temporal variability of methane emissions and environmental conditions in a hyper-eutrophic fishpond

“…However, these findings are based on studying mostly lakes whose morphology, trophic state or oxygen regime sharply contrast with the Dehtář fishpond, where the upper two meters of the water column were oxygen-saturated while the deepest strata were mostly anoxic. In such hyper-eutrophic systems, high nutrient loading increases autochthonous primary production (Potužák et al, 2007;Rutegwa et al, 2019) and promotes oxygen consumption and anaerobic decomposition in the sediments (Baxa et al, 2020), leading to enhanced CH4 production (Bastviken et al, 2004;Grasset et al, 2018). In aquaculture ponds in Southeast China, CH4 fluxes exhibited considerable spatial variations and peaked in the relatively deep feeding zone, where the large loads of sediment organic matter fueled CH4 production (Yang et al, 2020).…”