Treatment of a small stream impacted by agricultural drainage in a semi-constructed wetland

• Published in: The Science of the total environment 2018-12, Vol.643, p.52-62
• Main Authors: Vymazal, Jan, Dvořáková Březinová, Tereza
• Format: Article
• Language: English
• Subjects: Agricultural drainage; Nitrogen; Permanent flooding; Phosphorus; Wetland
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2018.06.148

During the period 2014–2016, removal of nutrients, organics and suspended solids from a small rural stream impacted by agricultural drainage in a natural and semi-constructed wetlands was evaluated. In 2014, the wetland was irregularly flooded during high flows in the stream, in 2015, the stream bed was cleaned and as a result the water level dropped down by about 0.5 m, thus no flooding occurred. In 2016, the stream was blocked and water was permanently diverted into a wetland dominated by Phalaris arundinacea, Carex nigra and Scirpus sylvaticus. The results clearly revealed a positive role of permanent flooding resulting in the highest removal of all monitored parameters, i.e. nitrogen (38%), phosphorus (40%), BOD5 (42%) and suspended solids (67%). The permanent flooding increased aboveground biomass of P. arundinacea and C. nigra while S. sylvaticus was eliminated by permanent flooding. The repeated harvest yielded higher aboveground biomass for P. australis and S. sylvaticus, while for C. nigra one harvest provided more biomass. In 2016, the removal expressed as the loading averaged 1102 kg TN ha−1 yr−1 and 894 kg NO3-N ha−1 yr−1 and the plant uptake was responsible for removal of 36.1% TN. The average removal of total phosphorus amounted to 164 kg P ha−1 yr−1 with plant uptake being responsible for 18.7%. Average removal of BOD5, COD and TSS amounted to 1108, 5953 and 9220 kg ha−1 yr−1, respectively. While the removal of BOD5 and COD increased exponentially with increasing water temperature, removal of TSS was not affected by water temperature. The results proved that slightly modified natural wetlands with negligible investment costs can be as effective as fully constructed wetlands to treat agricultural drainage. [Display omitted] •The best removal of nutrients was achieved under permanent flooding conditions.•Permanent flooding was beneficial for Phalarias arundinacea growth.•Repeated harvest resulted in higher nutrient accumulation in aboveground biomass.•Average removal of nitrogen amounted to 1102 kg TN ha−1 yr−1.•Plant uptake was responsible for 36% and 19% of the removed TN and TP, respectively.