The biological assessment and rehabilitation of the world’s rivers: an overview
The biological assessment of rivers i.e., their assessment through aquatic assemblages,
integrates the effects of multiple-stressors on these systems over time and is essential to evaluate
the integrity of ecosystems and establish recovery measures. However, it has been undertaken in
many countries since the 1990s, but not globally. And where national or multi-national monitoring
networks have gathered large amounts of data, the poor water body classifications have not
necessarily resulted in the rehabilitation of rivers. Thus, here we aimed to identify major gaps in the
biological assessment and rehabilitation of rivers worldwide by focusing on the best examples in
Asia, Europe, Oceania, North, Central and South America. Our study showed that it is not possible
so far to draw a world map of the ecological quality of rivers. Biological assessment of rivers and
streams is only implemented officially nation-wide and regularly in the European Union, Japan,
Republic of Korea, South Africa and the USA. In Australia, Canada, China, New Zealand and
Singapore it has been implemented officially at the state/province level (in some cases using
common protocols) or in major catchments or even only once at the national level to define reference
conditions (Australia). In other cases, biological monitoring is driven by a specific problem, impact
assessments, water licenses or the need to rehabilitate a river or a river section (as in Brazil, South
Korea, China, Canada, Japan, Australia). In some countries monitoring programs have only been
explored by research teams mostly at catchment or local level (e.g., Brazil, Mexico, Chile, China,
India, Malaysia, Thailand, Vietnam) or implemented by citizen science groups (e.g. Southern Africa,
Gambia, East Africa, Australia, Brazil, Canada). The existing large-extent assessments show a
striking loss of biodiversity in the last 2-3 decades in Japanese and New Zealand rivers (70% of fish
species threatened or endangered). A poor condition exists in 25% of South Korean’s rivers, half of
the European water bodies and 46% of USA rivers while in Australia 30% of the reaches sampled
were significantly impaired in 2006. Regarding river rehabilitation, higher implementation has
occurred in North America, Northern Europe, Japan, Singapore and Republic of Korea. Most
rehabilitation measures have been related to improving water quality and river connectivity for fish
or improvement of riparian vegetation. The limited extents of most rehabilitation measures (i.e., not
considering the entire catchment) often constrain the improvement of biological condition. Yet,
many rehabilitation projects also lack pre-and/or post-monitoring of ecological condition, which
prevents assessing the success and shortcomings of the recovery measures. Economic constraints
are the most cited limitation for implementing monitoring programs and rehabilitation actions,
followed by technical limitations, limited knowledge of the fauna and flora and their life history
traits (specially in Africa, South America, Mexico) and poor awareness by decision makers. On the
other hand, citizens involvement is recognized as a key to the success and sustainability of
rehabilitation projects. Thus, establishing rehabilitation needs, defining clear goals, tracking
progress towards achieving them, and involving local populations and stakeholders are key
recommendations for rehabilitation projects. Large-extent and long-term monitoring programs are
also essential to provide a realistic overview of the condition of rivers world-wide. Soon, the use of
DNA of biological samples and eDNA to investigate aquatic diversity could contribute to the reducing costs and thus increase monitoring efforts and a more complete assessment of biodiversity. (*** insufficient space see manuscript for final sentence***)