Paradox of nutrient removal in coupled socioeconomic and ecological dynamics for lake water pollution

Abstract

We study coupled socioeconomical and ecological dynamics for lake water pollution. Players choose between cooperative (but costly) option and economical option, and their decision is affected by the fraction of cooperators in the community and by the importance of water pollution problem. When an opportunity for choice arrives, players take the option with the higher utility (best response dynamics). This social dynamics is coupled with the dynamics of lake water pollution. First, oscillation of large amplitude is generated if social change occurs faster than ecosystem responses. Second, the model can show "paradox of nutrient removal". If phosphorus is removed more effectively either from the inflow or from the lake water, the pollution level may increase (rather than decrease) due to the decline in people's willingness to cooperate. Third, we compare the effectiveness of alternative methods in improving water quality: to reduce the cooperation cost by subsidy, to enhance people's concern to water pollution problem, and to promote the conformity among people.

Combined effects of social pressure from the inside and outside of fishing communities promote cooperation for stock management

“…Hence, the external social pressure becomes weaker if 1 À x is small. Although ''external social pressure'' is not considered in previous studies [e.g., Iwasa et al (2010)], we conclude that this kind of social pressure exists after careful consideration.…”

“…The solid arrows indicate the shifts of cases when the value of c increases, while the broken arrows indicate the shifts when k increases deterministic, that is, b is very large. The isocline becomes close to the following three segments as discussed in the coupled socioeconomic and ecological dynamics for lake water pollution (Iwasa et al 2010):…”

“…That is, external social pressure might have effect on players C as well as players N. In this case, it is likely that internal social pressure on players N from players C might become stronger and the difference in the two utility functions U C À U N might not change significantly from the case when the external social pressure has an effect only on players N. Hence, this viewpoint is not critical for the conclusion of the present study. Iwasa et al (2007Iwasa et al ( , 2010 referred to a paradox for lake water pollution. This paradox is that if phosphorous is removed more effectively either from the inflow or from the lake water, the pollution level may increase rather than decrease due to the decline in people's willingness to cooperate.…”

“…In such a situation, fishermen's self-esteem or reputation within the community can sometimes affect their fishing decisions (Platteau and Seki 2007). Iwasa et al (2007Iwasa et al ( , 2010 focused on ''social pressure'' and analyzed the interaction between people's cooperation and lake water pollution by means of a coupled socioeconomic and ecological dynamics model. In this model, people choose between an environmentally friendly option and an economical option, and their decision affects the pollution level of the lake water, which in turn affects people's decision-making.…”

“…In the present paper, we analyze community-based fisheries management by using the same method as coupled socioeconomic and ecological dynamics (Iwasa et al 2007(Iwasa et al , 2010). In the model, players (fishermen) choose whether to cooperate with management or not, depending on the utility of each option based on both fish yield and fishermen's psychological aspects.…”