The focus of this thesis is on the design of policy instruments to manage environmental issues, with a particular interest in dynamic taxation schemes and cap and trade systems in the context of irrigation-induced salinity. This issue is of crucial importance in most irrigated areas throughout the world. A first goal of the thesis is to investigate the use of dynamic taxation schemes based on a measure of group performance, as a way of implementing the notion of collective responsibility. The analysis focuses on the main characteristics of group performance based instruments, the interdependence they introduce among the agents. Indeed, when subject to group performance based instruments, agents' payoffs result from the effort providedby the group. The analysis is set at the catchment scale, and the collective result is the groundwater stock. Various taxes are investigated, including a time-independent standard input tax, a state-dependent ambient tax and a stock-dependent input tax. These taxes are illustrative of various ratios of individual performance and collective performance in the design of the policy instrument. One of the results of this analysis is that including a group performance component in the policy instrument is necessary to induce the agents to behave optimally along the whole time horizon. Hence the interest for mixing individual and collective incentives in the design of policy instruments. A second aim of the thesis is to address the design of cap and trade systems to manage multiple coupled externalities. The catchments are replaced within the broader context of the river system, and the analyses relate to the interactions developing between water management initiatives at the catchment and the river scales. To manage both water scarcity along the river and irrigation-induced salinity in each catchment, two types of water rights are considered : standard diversion rights and recharge rights that allow right-holders to produce a certain amount of percolation. This analysis poses the question of the number of policy instruments needed to manage correlated externalities. It also raises issues associated with the implementation of cap and trade systems at different scales. The main result of this analysis is that the correlation existing between the externalities doesn't rule out the need for a policy instrument to manage each externality. While the aim of this thesis isn't to compare these two policy strategies, by the analyses it provides it participates in the debate about the use of price-based or quantity-based instruments. Furthermore, the analyses apply to the general case of correlated environmental externalities.