Traditional common carp (Cyprinus carpio) farming, mainly realised in earthen ponds, functions highly embedded in the landscape and is regarded as a semi-natural ecosystem. Semi-intensive farming systems typically involve a three-year cycle for common carp production, in which fish rely on natural pond food and are additionally supplemented with locally produced cereals. To mitigate the environmental impact of carp farming, producers adhere to official regulations that limit carp production to 1500 kg increased biomass per hectare, considering the nutrient release effects . One of the objectives of SAFE project is to minimise the impact of pond farm on environment and improve the viability of the freshwater aquaculture by development of sound circular economy approaches . Therefore, to reduce the impact of the farms on the river systems and to increase profitability of the farms the SAFE team built a full-scale, low-cost, and low-tech system to capture sediments discharged from the farm. Moreover, we have assessed efficiency of the system to capture sediments, quality of the captured sediments and condition of the environment before and after application of the system.
System for sediment sequestration consisted of 69 barriers made of 3-set straw bricks arranged in a herringbone layout (136 m) and nailed to the bottom of the main discharge channel . The system has been in operation for the full period of pond emptying, i.e. from October of 2023 to January of 2024. Every week water parameters before and after the system, as well as at eight evenly distributed sampling sites were assessed on-site using multiparametric probe (e.g. pH, temperature) and water samples were collected and secured to perform additional hydrochemical analyses ( e.g. DO, NO3, NH3 , P, % of TSS). After the trial sediments sequestrated by the system were sampled and analysed to assess chemical and toxicological parameters as well as grain size. Next, sequestration efficiency of the systems has been assessed concerning weight sediment deposited between and inside the brick barriers. To assess whether the system have a positive impact on the biodiversity the communities of benthic macroinvertebrates were collected and assessed, as well as condition of three aquatic bioindicators (noble crayfish, Astacus astacus ; thick shelled river mussel, Unio crassus ; river water-crowfoot, Ranunculus fluitans ) installed downstream the system.
The system reduced speed of the discharged water (meandering ) and 85 tonnes of sediments settled between barriers. Moreover, each of the 207 straw bricks was infiltrated on average with 10 kg of discharged sediments. Laboratory analyses showed that sequestrated sediment did not contain pesticides, antibiotics and chemical composition and grain size distribution showed its potential as a substrate or co-substrate in agriculture or horticulture. The use of sediments has been already proved in a production of beta-glucan-rich oyster mushroom (Pleurotus ostreatus). Aquatic bioindicators installed downstream the sequestrating system survived the discharging period in good condition, showing that installation of the system brings ecological benefits.
Funding
This work was supported by the funding from the European Union’s Horizon Europe programme under grant agreement no. 101084549.