Japanese knotweed (Fallopia japonica) is a highly invasive species affecting the health and biodiversity of the native ecosystems throughout North America. Riparian zones are susceptible to invasion by knotweed and many streams in Abbotsford now have invasive knotweeds present. An important question to ask is, how does the input of knotweed leaves affect the macroinvertebrate community in streams? The relationship between stream macroinvertebrate populations and knotweed leaves was studied over three years using a stream where knotweed had not been found. Leaf litter bags were filled with 4.0 grams of air dried yellow or green leaves and placed in various sites around Clayburn Creek in Abbotsford, BC. All bags were tied to bricks and held in position using stakes. The bags were left in the stream for a total of 3 months, with removal of one bag from each site every seven days. The leaves were carefully cleaned in the lab and invertebrates were collected into vials containing 95% ethanol. They were then identified and tallied the following day. Water quality of the stream was monitored over the three year period. Nutrient analysis of the leaves was done and C:N ratios calculated.
Results/Conclusions
Leaf litter bags containing green Japanese knotweed leaves consistently had a greater species richness and overall diversity of macroinvertebrates than yellow leaves, and was consistent at all locations. This may be attributed to the relatively greater nitrogen content in green leaves, as was found from the nutrient analysis tests. These trends were consistent with the previous year’s data, as well. In contrast, no visible trends for species abundance was present and this may be due to various factors, such as large fluctuations in temperature, precipitation, and canopy coverage throughout and between the years. Additionally, comparison of different feeding types signified that the green leaves had more scrapers than the yellow leaves, indicating that the green leaves may have provided favourable conditions for algal growth. In conclusion, this study provides an important insight on how Japanese Knotweed leaves affect freshwater macroinvertebrate populations.