# Integrating Inland and Coastal Water Quality Data for Actionable Knowledge
## 3 Overview of Observational Methods and Platforms
### Discrete Sampling  
Discrete sampling has been used for decades to obtain information about physical, chemical, and biogeochemical parameters related to water quality [17]. Once on site, it is easy to deploy instruments, such as Secchi discs, optical sensors, conductivity, temperature, and depth sondes, and to collect discrete water samples using collection bottles, such as Niskins. These measurements (surface and vertical profiles) are made from the shoreline, boats, buoys, and automated vehicles at a single location or across transects, depending on the extent of the water body of interest and the aim of the sampling. The measurement protocols generally are very well defined, and the instruments are easy to handle and cost-effective [18; 19; 20; 21; 22; 23; 24; 25; 26]. After collection, water samples either are processed or filtered separately and typically preserved for further analysis in laboratories. The measured parameters provide information about autochthonous processes, the consequences of external inputs to these water bodies (salinity, pH, nutrients, particulate organic and suspended matter), and on the functioning of the ecosystem (dissolved oxygen and plankton biomass), leading to a comprehensive and extensive suite of analytes to assess the health of the water body. Grassroots networks and regional, and national programs have been developed for measuring and monitoring essential variables in nearshore coastal, estuarine, and inland waters (for example, the French monitoring network Service d'Observation en Milieu LITtoral (SOMLIT); the Global Lake Ecological Observatory Network (GLEON; [27]); and the European Ocean Observing System (EOOS)).  
However, discrete sampling can be costly in terms of human resources and use of equipment. Measurements are typically local and sampled over a very limited area and a short period. These measurements typically are limited to bi-weekly, monthly, or even quarterly surveys, often missing diurnal or day-to-day variability. This low frequency  
Figure 3: Schematic representation for the combination of (**a**) discrete, continuous, and citizen science measures combined with (**b**) remote sensing, and (**c**) modelling data. The combination provides complementary trade-offs of accuracy, number of parameters provided, spatial resolution, temporal frequency, and cost efficiency.  
means that measurements rarely characterize the variability of the water body of interest adequately and may be insufficient to detect spatial variability within the waterbody and trends over time unless conducted for many years. The water body also may be difficult to access, for example when far from accessible infrastructure, limiting the number of surveys and increasing the survey costs. There is often a lack of cyber-infrastructure to enable near real-time sharing of discrete data, whereas different instruments, sampling protocols, and quality assurance procedures are used across laboratories, organizations, and countries. There are also limited coordinating monitoring networks globally, such as the European Global Ocean Observing System (EuroGOOS) or the Fiducial Reference Measurements for Satellite Ocean Colour (FRM4 SOC) [28] across Europe, the National Water Quality Monitoring Network, or the Global Environment Monitoring System for Freshwater (GEMS/Water) or the National Water Quality Program in the United States.