A growing sense of an international environmental crisis has brought new attention to the field of environmental planning and policy, yet many of the planning techniques and policy mechanisms in the field reflect the characteristics of environ­ mental problems from the late 1960s and 1970s. The chal­ lenges of the 1990s are quite different from those facing envi­ ronmental planning and regulatory agencies when those agen­ cies were first established, and several emetging trends could compel new approaches to environmental planning and poli­ cy. This article discusses five major trends and their implica­ tions for environmental planning and policy in the coming decade. Together, these trends will require environmental policymakers to rely more upon incentives-based regulatory approaches that address the cumulative .efectf of many small, dispersed, ubiquitous emission sources that could have global impacts. Thisnewchallengecontrastssharplywiththehistoric regulatory approach in the United States, which has empha­ sized technology-oriented, standards-based, command-and­ control regulation oflarge, centralizedpoint sources ofpoilu· tion emissions. Unless environmental planning and policy institutions adapt to this new environment, however, they will not succeed.

In the past four decades, the migration of urban and suburban dwellers into rural areas of the United States has dramatically transformed the social, economic, and ecological conditions in rural areas. This migration places development pressure on forested,

agricultural, and open space areas and leads to the subdivision of large tracts of land into smaller parcels, which can complicate the governance and management of human- environmental problems.

The prevention and control of nonpoint source (NPS) pollution

from rural private lands is a particularly pressing human-environmental challenge that may be exacerbated by the growing number and diversity of rural landowners. Reducing NPS pollution is increasingly dependent on understanding how to promote the adoption of pollution control measures (known as best management practices [BMPs]) by a growing and diverse group of private landowners.

In this dissertation, I address this governance challenge through an investigation of how regulations, non-regulatory programs, and other factors promote and impede the adoption of BMPs by different groups of landowners. I focus on the prevention and control of sediment (a common NPS pollutant) from private timber, ranch, residential, and

marijuana producing lands in the rural North Coastal Basin of California. This research utilizes an institutional analysis approach and employs a combination of qualitative and quantitative methods applied at the watershed and regional scale.

Though the sediment pollution problem is associated with management practices on all land uses, this research reveals that sediment pollution is unevenly governed. I find that that the stringency and enforcement of regulations, influence of non-regulatory programs, and landowners' knowledge and adoption of BMPs vary by land use. Landowners engaging in traditional rural land uses such as timber production and ranching are generally more knowledgeable about BMPs than other landowners. Their use of BMPs is associated with strictly enforced regulations and/or participation in non-regulatory programs. Residential landowners and those using their land for marijuana cultivation receive less attention from resource agencies and non-governmental organizations and are less likely to be familiar with BMPs. Consequently, as residential uses and marijuana cultivation become more common across the region, these parts of the landscape become ungoverned leaving the area vulnerable to increases in NPS pollution.

The challenges of governing and managing sediment pollution in the transitioning rural region of the North Coastal Basin mirror the challenges associated with the governance of many complex and evolving human-environmental problems. In this dissertation, I

focus on the social and institutional aspects of governance and management of these problems. In doing so, I draw attention to the ways that social complexity can complicate the governance of biophysically complex problems, highlight the influence of formal and

informal social interactions on landowners' management decisions, and add insight into the design of regulatory and non-regulatory programs that recognize and capitalize on the social factors that affect management decisions on private lands.