by Rohan Nath
Invasive or alien species are notorious for disturbing ecosystems across the world. Invasive species are capable of having large ecological and financial impacts. This can affect the ecological services provided by the nature and also local economic systems which involve the practice of subsistence agriculture and harvest of biological resources.
Shackleton et al. (2007) suggested that the impact of invasive species depends on factors like the density and rate of spread of the invasive species, how the local economies incorporate them as beneficial elements as firewood or food, and the vulnerability of the local communities. Invasive species can hamper the environment affecting the livelihoods which in turn determines the vulnerability of the community. Dependency upon subsistence agriculture, lack of household savings and reliance upon products obtained from the ecosystems. Invasive species greatly alter the local ecosystems and human communities with little resilience to ecological changes.
Intensive studies have been performed on floating aquatic plants as an invasive species and their impact on human communities. In freshwater systems, other factors like altered flow regimes, increased nutrient levels and the extinction of top predators due to overharvesting can enhance the spread, growth and impacts of invasive species. The removal of invasive species can vastly improve the ecosystem.
Floating plant species like Azolla cristata and Alternanthera philoxeroides (alligator weed) have severely invaded Wular Lake in Jammu and Kashmir (Fig. 1, 2). Regardless of a long history of environmental changes, many of these problems can be solved at a reasonable price.
The Wular Lake ecosystem
Wular Lake is the largest freshwater lake in India with a maximum surface area of 61.7 km2 and an elevation of 1580 m in the Kashmir Valley. Jhelum River brings an inflow of water from the neighbouring Himalayan and Pir Panjal mountain ranges. The season determines the flow of water with the highest flow during late spring and early summer due to high rainfall and snowmelt.
Bandipora and Baramulla are two administrative districts that border the lake with an increase of population by 4 and 3.5 times, respectively. These districts have a low education level as well as high poverty rates. 11,000 households belonging to 31 villages along the shoreline are highly dependent upon fishing, extraction of water and aquatic plants from the lake. Nelumbo (Nelumbo nucifera) and water chestnut (Trapa natans) are mainly harvested and used as human food and wetland grasses like Nymphoides peltata, Phragmites sp. as fodder.
Changes in the ecosystem
The increase in human population affects the land-use changes across the Kashmir valley (Table 1). Anthropogenic activities include increased quarrying activity, decreased forest area as trees are cut for fuel and to make way for settlement and agriculture, and encroachment of willow plantations and agricultural fields into wetlands
|Erosion risk in the Kashmir valley||48.3%|
|Dense forest decrease||26% to 16%|
|Bare land area||5.1% to 8.9%|
|Agricultural area||12.3% to 15.8%|
|Horticulture area||1.6% to 5.9%|
An increase in nutrient levels have been reported from the lake possibly due to increased agricultural fertilizer use and decreased filtering by wetlands. The lake is now classified as eutrophic due to an increase in the concentration of phosphorous and nitrogen. The seasonal phosphorous concentrations in the lake increased between 1992 to 2011 from 0.0-103 µg/L to 102-297 µg/L.
The emergence, growth and effect of two new floating aquatic plants as invasive species
The first report of Azolla cristata in Wular Lake was between 2002 and 2004 when it already started spreading, outcompeting other aquatic plants, and hindering navigation. It has formed a mat of 10 cm in thickness. The fishermen have to hire additional labour to help remove the mat from the water surface for proper navigation and casting of their nets.
The first report of Alligator weed in Wular Lake was in 2008. The dense floating patches of the plant hampers oxygen and light penetration and promote flooding and sedimentation. Six alligator weed patches have grown between 2008 to 2011 from an area of 41.3 m2 to 82 patches with an area of 831 m2. It is expected that 90% of the Wular Lake would be covered with alligator weed by 2027.
Interviews were conducted with the local population to gain an insight into the situation:
i. An 80-year-old fisherman stated that “Life was better before the weeds were here, there was more fish and people were happier. I now lament the current state of affairs of this lake. We don’t get help from the government and we cannot manage these weeds as we have to make a living and the returns are too low for hard work.”
ii. Another fisherman describes “In the last couple of years 600-700 fisherman have migrated from these villages to Srinagar (the capital city) because weeds reduce fishing, water quality, and increase water-borne disease. The lake has silted up and
fishing is worse, and there has also been a loss of water surface area and the ability to harvest Trapa (water chestnuts) so some fishermen now harvest sand for a living.”
Method to control
It is possible to control the spread of alligator weed which is still at an early stage of invasion in Wular Lake. Both A. cristata and alligator weed can be manually controlled since patches are easy to locate and the entire plant can be removed.
The manual control of invasive species can have the following benefits:
i. The provisioning of the ecosystem services would be safeguarded. ii. It would lead to the employment of the locals for removing the weeds, leading to an economical gain for the population.
iii. The other neighbouring ecosystems would be safe from the rapidly spreading invasive species.
iv. The establishment of invasive species removal program would allow the locals to be ready for future threats.
There should be more intensive studies to understand the impacts of invasive species on human well-being as well as ecological and economic impacts.
1. Keller, R. P., Masoodi, A., & Shackleton, R. T. (2018). The impact of invasive aquatic plants on ecosystem services and human well-being in Wular Lake, India. Regional environmental change, 18(3), 847-857.