--- title: "Dissolved Load in Earth Systems Science" description: "Dissolved load is the part of river sediment carried as ions in water, shaping watershed chemistry, weathering signals, and water quality in Earth Systems Science." canonical: "https://fiveable.me/earth-systems-science/key-terms/dissolved-load" type: "key-term" subject: "Earth Systems Science" unit: "Unit 6" --- # Dissolved Load in Earth Systems Science ## Definition Dissolved load is the portion of a river’s load carried in solution, mostly as ions like calcium, sodium, bicarbonate, and sulfate. In Earth Systems Science, it shows how weathering, runoff, and water chemistry move material through a watershed. ## What It Is Dissolved load is the material a river carries that you cannot see as separate particles because it is dissolved in the water. In Earth Systems Science, that usually means ions released when rocks and soils weather, such as calcium, magnesium, sodium, potassium, bicarbonate, and sulfate. The river is still transporting sediment, just in a chemical form instead of as visible grains. This is different from sand, silt, and clay moving as suspended load or from pebbles and larger clasts rolling along as bedload. Dissolved load comes from chemical weathering, where water reacts with minerals and breaks them down into ions. Rainwater picks up carbon dioxide from the air and soil, forming weak carbonic acid, which helps dissolve minerals as water moves through a watershed. The amount of dissolved load changes with geology, climate, and land use. A watershed with lots of easily weathered rock, warm temperatures, and abundant rainfall usually produces more dissolved ions than a dry region with resistant bedrock. During storms or snowmelt, more water moves through soil and rock, so dissolved load can increase even if the water looks muddy or clear. Rivers carry dissolved load all the way downstream to lakes, estuaries, and oceans. That matters because these ions affect water hardness, buffering capacity, salinity, and nutrient cycling. For example, bicarbonate helps control how acidic or basic water becomes, while calcium and magnesium are common in waters draining limestone and other carbonate rocks. A useful way to think about dissolved load is that it is a chemical fingerprint of the watershed. If a river shows unusual changes in ion concentration, scientists may look for shifts in weathering rates, groundwater input, agricultural runoff, road salt, or other human influences. That makes dissolved load a big clue in river chemistry, not just a label for what is dissolved in the water. ## Why It Matters Dissolved load shows how the geosphere and hydrosphere are linked. Weathering does not just break rock into smaller pieces, it also turns solid minerals into ions that move through streams and rivers. That makes dissolved load one of the clearest ways to track chemical weathering and material transfer inside a watershed. It also connects to water quality. The ion mix in a river affects hardness, acidity, and how well the water buffers pH changes. If you are looking at land use impacts, dissolved load can reveal things like fertilizer runoff, mining drainage, wastewater input, or road salt entering the stream. In Earth Systems Science, this term helps you compare different kinds of river transport. A muddy flood might raise suspended load, but dissolved load can stay high even when the river looks clear. That difference matters when you are interpreting hydrographs, watershed diagrams, lab data, or explanations of how rivers move matter from land to sea. ## Connections ### Suspended Load Suspended load is sediment carried as tiny particles floating in the water column. Unlike dissolved load, it is not chemically dissolved, so you can often measure it by filtration or see it as cloudiness after a storm. The two often increase together during runoff, but they describe different forms of transport. ### Bedload Bedload is the coarsest part of a river’s load, made of particles that roll, slide, or bounce along the channel bottom. It moves very differently from dissolved load because it depends on flow strength and particle size, not on chemical weathering. If a river slows down, bedload drops out first, while dissolved ions stay in solution. ### [Drainage Basin](/earth-systems-science/key-terms/drainage-basin) A drainage basin is the land area that funnels water and dissolved materials into one river system. Dissolved load is one of the main outputs of that basin, so the rock type, soil, slope, and land use inside the basin all affect what ions end up in the stream. That is why watershed boundaries matter in river chemistry. ### River Discharge River discharge is the volume of water flowing past a point in a given time, and it affects how much dissolved material a river can carry downstream. High discharge after rain or snowmelt often increases total ion transport, even if concentration does not always rise at the same rate. This is why dissolved load is often discussed alongside flow. ## On the AP Exam A quiz item might give you a river graph, water chemistry table, or watershed scenario and ask you to identify which part of the load is being described. You would pick dissolved load when the question talks about ions, minerals in solution, or changes in water chemistry rather than visible sediment. In a short-answer or lab context, you might compare two streams and explain why one has higher dissolved load because of limestone geology, more chemical weathering, or greater groundwater input. If the class uses water-quality data, you may need to interpret ion concentration, salinity, or hardness as evidence of dissolved load. You may also be asked to separate dissolved load from suspended load and bedload in a diagram or data set. The move is simple: look for particle size, visibility, and whether the material is chemically dissolved or physically carried. ## dissolved load vs suspended load Suspended load and dissolved load both move through river water, so they get mixed up a lot. The difference is that suspended load is made of tiny solid particles that can be filtered out, while dissolved load is made of ions in solution. If the water is cloudy, think suspended load. If the material is invisible but chemically present, think dissolved load. ## Key Takeaways - Dissolved load is the part of a river’s load carried in solution, not as visible sediment. - It mostly comes from chemical weathering of rocks and soils, which releases ions into water. - The amount of dissolved load changes with geology, climate, runoff, groundwater input, and land use. - Dissolved load affects water chemistry, including hardness, acidity, buffering, and nutrient cycling. - If you are comparing river transport, dissolved load is different from suspended load and bedload. ## FAQs ### What is dissolved load in Earth Systems Science? Dissolved load is the material a river carries as dissolved ions in the water. It comes mainly from weathering of rocks and soils, so it tells you something about the chemistry of the watershed. Unlike sand or silt, it is not visible as separate particles. ### How is dissolved load different from suspended load? Suspended load is made of tiny solid particles floating in moving water, while dissolved load is made of ions dissolved in the water itself. A filter can remove suspended load, but not dissolved ions. Both are part of river transport, but they come from different processes and show up differently in data. ### Where does dissolved load come from? It mainly comes from chemical weathering. Water reacts with minerals in rock and soil, releasing ions like calcium, sodium, bicarbonate, and sulfate. Groundwater can also contribute because it has spent time in contact with rock and often picks up more dissolved ions. ### How do you measure dissolved load in a river? You usually measure water chemistry, not visible sediment. Scientists sample river water, filter out particles, and test the dissolved ions using lab methods or conductivity readings. Changes in those values can show shifts in rainfall, geology, pollution, or land use. ## Related Study Guides - [6.3 River systems and watershed dynamics](/earth-systems-science/unit-6/river-systems-watershed-dynamics/study-guide/2pUpzQ8IsmW8yz6r) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/earth-systems-science/key-terms/dissolved-load#resource","name":"Dissolved Load in Earth Systems Science","url":"https://fiveable.me/earth-systems-science/key-terms/dissolved-load","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/earth-systems-science/key-terms/dissolved-load#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:21:25.274Z","isPartOf":{"@type":"Collection","name":"Earth Systems Science Key Terms","url":"https://fiveable.me/earth-systems-science/key-terms"},"author":{"@type":"Organization","@id":"https://fiveable.me/editorial#content-team","name":"Fiveable Content Team","url":"https://fiveable.me/editorial","parentOrganization":{"@id":"https://fiveable.me/#organization"},"member":[{"@type":"Person","name":"Amanda DoAmaral","sameAs":["https://www.linkedin.com/in/adoamaral"]},{"@type":"Person","name":"Becky Bahr","sameAs":["https://www.linkedin.com/in/becky-bahr-b52743132"]}]},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/earth-systems-science/key-terms/dissolved-load#term","name":"dissolved load","description":"Dissolved load is the portion of a river’s load carried in solution, mostly as ions like calcium, sodium, bicarbonate, and sulfate. In Earth Systems Science, it shows how weathering, runoff, and water chemistry move material through a watershed.","url":"https://fiveable.me/earth-systems-science/key-terms/dissolved-load","inDefinedTermSet":{"@type":"DefinedTermSet","name":"Earth Systems Science Key Terms","url":"https://fiveable.me/earth-systems-science/key-terms"}},{"@type":"FAQPage","mainEntity":[{"@type":"Question","name":"What is dissolved load in Earth Systems Science?","acceptedAnswer":{"@type":"Answer","text":"Dissolved load is the material a river carries as dissolved ions in the water. It comes mainly from weathering of rocks and soils, so it tells you something about the chemistry of the watershed. Unlike sand or silt, it is not visible as separate particles."}},{"@type":"Question","name":"How is dissolved load different from suspended load?","acceptedAnswer":{"@type":"Answer","text":"Suspended load is made of tiny solid particles floating in moving water, while dissolved load is made of ions dissolved in the water itself. A filter can remove suspended load, but not dissolved ions. Both are part of river transport, but they come from different processes and show up differently in data."}},{"@type":"Question","name":"Where does dissolved load come from?","acceptedAnswer":{"@type":"Answer","text":"It mainly comes from chemical weathering. Water reacts with minerals in rock and soil, releasing ions like calcium, sodium, bicarbonate, and sulfate. Groundwater can also contribute because it has spent time in contact with rock and often picks up more dissolved ions."}},{"@type":"Question","name":"How do you measure dissolved load in a river?","acceptedAnswer":{"@type":"Answer","text":"You usually measure water chemistry, not visible sediment. Scientists sample river water, filter out particles, and test the dissolved ions using lab methods or conductivity readings. Changes in those values can show shifts in rainfall, geology, pollution, or land use."}}]},{"@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Earth Systems Science","item":"https://fiveable.me/earth-systems-science"},{"@type":"ListItem","position":2,"name":"Key Terms","item":"https://fiveable.me/earth-systems-science/key-terms"},{"@type":"ListItem","position":3,"name":"Unit 6","item":"https://fiveable.me/earth-systems-science/unit-6"},{"@type":"ListItem","position":4,"name":"dissolved load"}]}]} ```