# The Biological Assessment and Rehabilitation of the World's Rivers: An Overview
## 2 Biological Assessment of Rivers
### Asia  
Biological monitoring of rivers is not a common approach in the majority of Asian countries, instead, monitoring of freshwater quality is primarily undertaken via traditional physiochemical and microbial measurements. However, it is applied in Japan, South Korea, Singapore and China to different degrees ([77; 78; 79]; Table S1). In Japan, the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), having responsibility for 109 major Japanese river systems, launched the Nature-oriented river works in the 1990s [80]. At the same time, MLIT initiated the National Census on the River Environment (NCRE) to gather nation-wide baseline information on the ecological state of river corridors. Following standardized protocols, data on fish, benthic invertebrates, plants, birds, terrestrial insects, amphibians, reptiles and mammals are collected from 109 Class A and 133 Class B rivers at five (or ten)-year intervals. All data are checked through a rigorous peer-review process and made publicly available in a river environmental database ([[http://www.nilim.go.jp/lab/fbg/ksnkankyo/](http://www.nilim.go.jp/lab/fbg/ksnkankyo/)]([http://www.nilim.go.jp/lab/fbg/ksnkankyo/](http://www.nilim.go.jp/lab/fbg/ksnkankyo/))). This regular monitoring not only provides important information on long-term trends in biodiversity but also improves scientific understanding of river ecosystems [81]. It provides important baseline information to support River Improvement Plans (basic plans for river management for 20-30 years) and to identify priorities for river rehabilitation. The long-term NCRE results(ca. 30 years) indicate a decline in riparian biodiversity, invasion of non-native species and a decline in the number of spawning bitterlings [82]. However, the lack of reference sites and ecological quality goals are considered drawbacks when compared with other monitoring programs. The limited number and area of NCRE survey points for each river, however, preclude planning reach-extent rehabilitation projects and having a catchment-scale biodiversity perspective. Therefore, the MLIT began a pilot-study in 2019 using environmental DNA to investigate fish diversity with the goal of costs reduction and increased number of monitoring sites. Additionally, Airborne Lidar bathymetry (ALB) has been used for river surveys and allowed to facilitate three-dimensional habitat distribution and watershed-scale ecological niche modelling. In the Republic of Korea, guidelines for aquatic ecology surveys are in operation to evaluate river rehabilitation projects. The legal basis for these guidelines is governed by the Water Environment Conservation Act. The Enforcement Rules of this Act stipulate surveys of aquatic ecosystem health. South Korea's National Aquatic Ecological Monitoring Program (NAEMP) began research in 2003 and was implemented on 540 to 800 sites annually. In 2009, its results indicated that 2%, 9%, 25% and 25% of sites scored as poor based on riparian, macroinvertebrate, fish and diatom MMIs, respectively. The Water Quality and Aquatic Ecosystem Conservation Act stipulated a survey on ecological health, covering over 3000 sites. The Guidelines for the Survey of Aquatic Ecology and Methods for Health Assessment stipulate assessing diatoms (Trophic Diatom Index), benthic macroinvertebrates (Benthic Macroinvertebrate Index) and riparian vegetation (Riparian Vegetation Index). All three indices include species composition and other metrics such as: diatom abundance per species; number of macroinvertebrate endemic, sensitive, tolerant, abnormal and hybrid species; and vegetation cover, area of annual plants, presence of non-native species, species evenness of hygrophytic plants and number of tolerant species for riparian vegetation. The reference values of the indices are adjusted to the natural characteristics of Korea's rivers and past monitoring results and research. The Singapore Public Utilities Board conducts regular water quality monitoring across canals, rivers and reservoirs [78].