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Environmental monitoring has a long history and has been a cornerstone in the development of the fields of hydrology, contaminant transport, air quality, ecology, and more. Monitoring is the ongoing observation, recording, and characterization of a site, process, or variable (Figs. 2.9 and 2.10). This type of research allows trends (directional patterns) to be detected and evaluated and typically these studies gain power and reliability as they become more prolonged and as the frequency of measurements increases. For agricultural and environmental field research, single seasons of observation can be influenced by the unique weather conditions or distinct events occurring within that period. This can constrain the conclusions which may be drawn from that study and may limit or influence how they can be applied to a broader context or to other situations. Furthermore, many environmental changes are relatively slow, having innate time lags due to geographic scale, rate of water movement, length of breeding cycles, and a host of other factors. Monitoring over sufficiently long periods is therefore essential to evaluate both environmental impacts and the processes which influence them (Fig. 2.11). Field monitoring is often used to determine compliance with environmental legislation and to supply evidence for the enforcement of those laws.

Fig. 2.10 This phenocam at Konza Prairie, Kansas, provides automated recording of plant canopies and is part of a network across the United States and Canada. Collections of case studies using identical methods can allow greater conclusions to be drawn.

Source: Sara Vero

Fig. 2.11 Monitoring infrastructure such as the weather station at this farm research platform in the United Kingdom can be powered by solar panels. These reduce the need for frequent battery replacement and are capable of supporting relatively demanding equipment. Also seen here is a livestock‐proof fence ‐ essential for preventing damage to the weather station.

Source: Sara Vero.

Hydrology is perhaps notable for utilizing long‐term monitoring studies, some spanning over multiple decades. Perhaps this stems from our current and historic reliance on watercourses for abstraction, transport, and fishing and conversely, the potentially catastrophic threat of floods. The River Thames in London, U.K. is an example of long‐term monitoring and provides the longest record of water chemistry in the world. Monthly nitrate concentrations have been recorded for over 140 years, starting in 1868, accompanied by weather records for the same period and discharge since 1884. This remarkable record was investigated and documented by Howden et al. (2010), but the initiation of the monitoring was done by drinking water treatment works supplying the city of London. The engineers who established this likely had no idea that the records they began would provide insight into the environmental consequences of population increases throughout the 20th century, the advent of chemical fertilizers, World War I and II, land‐use changes, the establishment of the European Union and the water and agricultural laws brought in thereafter. While the extensive record allows each of these historical events to be examined, it also informs the design of other monitoring endeavors. For example, by evaluating the rate of hydrochemical change, the authors of that study determined that studies of shorter than 15 years would be vulnerable to error if lacking appropriate historical context. The design of legislation also depends on this evidence to guide expectations of environmental responses, which may not correspond to governance or election cycles. The definition of “long term” research varies between disciplines; however, some general consensus appears to be around 10–15 years. Lindenmayer and Likens (2010) proposed a 10‐yr threshold for ecological monitoring.

While no strict rule or agreed convention exists, short‐term monitoring may lend itself more to case studies, while increasing length and frequency of monitoring allows application of more statistical analyses.

Monitoring studies can take different approaches including (but not limited to):

 Repeated physical sampling of water, soil, or vegetation for analysis at the laboratory. This samples can be obtained directly by a researcher in the field, or by automated samplers.

 Use of sensors at appropriate temporal resolution for measurements such as temperature, river discharge, turbidity, eddy covariance, etc. Sensors often facilitate high‐temporal resolution monitoring up to sub‐hourly frequency.

 In situ measurements (often coupled with electronic sensors and validated against laboratory samples). Monitoring at river outlets may take this approach, in which bankside devices automatically extract samples from the watercourse and analyze them on location for nitrogen and phosphorus.

 Observational monitoring may be used for wildlife studies. This can take the form of GPS tagging of birds, fish, or animals, the use of catch‐and‐release traps, or of field cameras to observe activity and behavior.

Monitoring can be expensive including the initial outlay for establishment of the experiment, its ongoing maintenance and its high demand for consumables. Large monitoring endeavors often require dedicated staff for maintenance of equipment. However, these challenges can be overcome and increasingly the value of monitoring studies is appreciated, particularly for providing baseline or background data for other research.

There are a number of groups and consortiums comprising discrete monitoring projects who collaborate across sites or adhere to agreed standards, measurements, and protocols. These programs might focus on one particular field of research or may take an integrative approach incorporating many distinct fields. As an example, the Long‐Term Ecological Research (LTER) Network includes 26 independent research sites funded by the U.S. National Science Foundation (NSF) since 1980. These sites represent a breadth of ecosystems including tallgrass prairie (Konza, Kansas), the Antarctic (Palmer Station, Anvers Island), and marine (California Current). The Long‐Term Agroecosystem Research (LTAR) network created by the USDA Agricultural Research Service (USDA‐ARS) similarly co‐ordinates 18 independent sites across the contiguous United States. The goal of LTAR is to investigate and develop strategies for the sustainability of agricultural production under the three pillars of productivity, environment, and rural prosperity.

These distinct sites follow a consistent approach to data collection across the entire network, although specific measured variables are selected as appropriate to each site (for example, depth of permafrost is measured at the Artic site but would be irrelevant for the urban biome in Arizona). These measurements allow conceptual understanding of these ecosystems, development of ecological, hydrologic, and biogeochemical models, and collaborative investigations across contrasting environments. Ambitious research programs such as these support long‐term monitoring over multiple decades from which projections into the future can be modeled and act as a benchmark against which comparable sites can be evaluated. Furthermore, they provide well‐characterized, representative, and secure facilities in which controlled and replicated experiments can be executed. An example of this is the watershed‐scale tallgrass prairie experiment that has been conducted at the Konza Prairie LTER site in Kansas. In that experiment, 60 hydrologic watersheds have been subject to treatments including bison and cattle grazing, and five burn frequencies (annual, 2‐yr, 4‐yr, 20‐yr, and >20‐yr intervals, in addition to no‐burning) since the establishment of the facility in 1972 (it later became one of the six founding LTER sites in 1980). These treatments have provided insights into the implications of management for the remaining US prairie grasslands and species.